Documentation/technical/protocol-v2.txt: fix formatting

Asciidoctor versions v1.5.7 or later print the following warning while
building the documentation:

      ASCIIDOC technical/protocol-v2.html
  asciidoctor: WARNING: protocol-v2.txt: line 38: unterminated listing block

This highlights an issue (even with older Asciidoctor versions) where
the 'Initial Client Request' header is not rendered as a header but in
monospace.  I'm not sure what exactly causes this issue and why it's
an issue only with this particular header, but all headers in
'protocol-v2.txt' are written like this:

   Initial Client Request
  ------------------------

i.e. the header itself is indented by a space, and the "underline" is
two characters longer than the header.

Dropping that indentation and making the length of the underline match
the length of the header apparently fixes this issue.

While at it, adjust all other headers 'protocol-v2.txt' as well, to
match the style we use everywhere else.

The page rendered with AsciiDoc doesn't have this formatting issue.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/protocol-v2.txt

@@ -1,5 +1,5 @@
- Git Wire Protocol, Version 2
-==============================
+Git Wire Protocol, Version 2
+============================
 
 This document presents a specification for a version 2 of Git's wire
 protocol.  Protocol v2 will improve upon v1 in the following ways:
@@ -22,8 +22,8 @@ will be commands which a client can request be executed.  Once a command
 has completed, a client can reuse the connection and request that other
 commands be executed.
 
- Packet-Line Framing
----------------------
+Packet-Line Framing
+-------------------
 
 All communication is done using packet-line framing, just as in v1.  See
 `Documentation/technical/pack-protocol.txt` and
@@ -34,8 +34,8 @@ In protocol v2 these special packets will have the following semantics:
   * '0000' Flush Packet (flush-pkt) - indicates the end of a message
   * '0001' Delimiter Packet (delim-pkt) - separates sections of a message
 
- Initial Client Request
-------------------------
+Initial Client Request
+----------------------
 
 In general a client can request to speak protocol v2 by sending
 `version=2` through the respective side-channel for the transport being
@@ -43,22 +43,22 @@ used which inevitably sets `GIT_PROTOCOL`.  More information can be
 found in `pack-protocol.txt` and `http-protocol.txt`.  In all cases the
 response from the server is the capability advertisement.
 
- Git Transport
-~~~~~~~~~~~~~~~
+Git Transport
+~~~~~~~~~~~~~
 
 When using the git:// transport, you can request to use protocol v2 by
 sending "version=2" as an extra parameter:
 
    003egit-upload-pack /project.git\0host=myserver.com\0\0version=2\0
 
- SSH and File Transport
-~~~~~~~~~~~~~~~~~~~~~~~~
+SSH and File Transport
+~~~~~~~~~~~~~~~~~~~~~~
 
 When using either the ssh:// or file:// transport, the GIT_PROTOCOL
 environment variable must be set explicitly to include "version=2".
 
- HTTP Transport
-~~~~~~~~~~~~~~~~
+HTTP Transport
+~~~~~~~~~~~~~~
 
 When using the http:// or https:// transport a client makes a "smart"
 info/refs request as described in `http-protocol.txt` and requests that
@@ -79,8 +79,8 @@ A v2 server would reply:
 Subsequent requests are then made directly to the service
 `$GIT_URL/git-upload-pack`. (This works the same for git-receive-pack).
 
- Capability Advertisement
---------------------------
+Capability Advertisement
+------------------------
 
 A server which decides to communicate (based on a request from a client)
 using protocol version 2, notifies the client by sending a version string
@@ -101,8 +101,8 @@ to be executed by the client.
     key = 1*(ALPHA | DIGIT | "-_")
     value = 1*(ALPHA | DIGIT | " -_.,?\/{}[]()<>!@#$%^&*+=:;")
 
- Command Request
------------------
+Command Request
+---------------
 
 After receiving the capability advertisement, a client can then issue a
 request to select the command it wants with any particular capabilities
@@ -137,8 +137,8 @@ command be executed or can terminate the connection.  A client may
 optionally send an empty request consisting of just a flush-pkt to
 indicate that no more requests will be made.
 
- Capabilities
---------------
+Capabilities
+------------
 
 There are two different types of capabilities: normal capabilities,
 which can be used to to convey information or alter the behavior of a
@@ -153,8 +153,8 @@ management on the server side in order to function correctly.  This
 permits simple round-robin load-balancing on the server side, without
 needing to worry about state management.
 
- agent
-~~~~~~~
+agent
+~~~~~
 
 The server can advertise the `agent` capability with a value `X` (in the
 form `agent=X`) to notify the client that the server is running version
@@ -168,8 +168,8 @@ printable ASCII characters except space (i.e., the byte range 32 < x <
 and debugging purposes, and MUST NOT be used to programmatically assume
 the presence or absence of particular features.
 
- ls-refs
-~~~~~~~~~
+ls-refs
+~~~~~~~
 
 `ls-refs` is the command used to request a reference advertisement in v2.
 Unlike the current reference advertisement, ls-refs takes in arguments
@@ -199,8 +199,8 @@ The output of ls-refs is as follows:
     symref = "symref-target:" symref-target
     peeled = "peeled:" obj-id
 
- fetch
-~~~~~~~
+fetch
+~~~~~
 
 `fetch` is the command used to fetch a packfile in v2.  It can be looked
 at as a modified version of the v1 fetch where the ref-advertisement is
@@ -444,8 +444,8 @@ header.
 		2 - progress messages
 		3 - fatal error message just before stream aborts
 
- server-option
-~~~~~~~~~~~~~~~
+server-option
+~~~~~~~~~~~~~
 
 If advertised, indicates that any number of server specific options can be
 included in a request.  This is done by sending each option as a