pack.indexversion config option now defaults to 2

As announced for 1.6.0.

Git older than version 1.5.2 (or any other git version with this option
set to 1) may revert to version 1 of the pack index by manually deleting
all .idx files and recreating them using 'git index-pack'.  Communication
over the git native protocol is unaffected since the pack index is never
transferred.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/asciidoc.conf

@@ -8,6 +8,7 @@
 # the command.
 
 [attributes]
+asterisk=*
 plus=+
 caret=^
 startsb=[

Documentation/config.txt

@@ -937,9 +937,17 @@ pack.indexVersion::
 	legacy pack index used by Git versions prior to 1.5.2, and 2 for
 	the new pack index with capabilities for packs larger than 4 GB
 	as well as proper protection against the repacking of corrupted
-	packs.  Version 2 is selected and this config option ignored
-	whenever the corresponding pack is larger than 2 GB.  Otherwise
-	the default is 1.
+	packs.  Version 2 is the default.  Note that version 2 is enforced
+	and this config option ignored whenever the corresponding pack is
+	larger than 2 GB.
++
+If you have an old git that does not understand the version 2 `{asterisk}.idx` file,
+cloning or fetching over a non native protocol (e.g. "http" and "rsync")
+that will copy both `{asterisk}.pack` file and corresponding `{asterisk}.idx` file from the
+other side may give you a repository that cannot be accessed with your
+older version of git. If the `{asterisk}.pack` file is smaller than 2 GB, however,
+you can use linkgit:git-index-pack[1] on the *.pack file to regenerate
+the `{asterisk}.idx` file.
 
 pack.packSizeLimit::
 	The default maximum size of a pack.  This setting only affects

pack-write.c

@@ -2,7 +2,7 @@
 #include "pack.h"
 #include "csum-file.h"
 
-uint32_t pack_idx_default_version = 1;
+uint32_t pack_idx_default_version = 2;
 uint32_t pack_idx_off32_limit = 0x7fffffff;
 
 static int sha1_compare(const void *_a, const void *_b)