Change git-gc documentation to reflect gc.packrefs implementation.

56752391a8 (Make "git gc" pack all
refs by default) changed the default of gc.packrefs to true, to
pack all refs by default in any repository.  IOW, the users need
to disable it explicitly if they want to by setting the config
variable, since 1.5.3.

However, we forgot to update the documentation.  This fixes it.

Signed-off-by: Florian La Roche <laroche@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-gc.txt

@@ -90,9 +90,9 @@ how long records of conflicted merge you have not resolved are
 kept.  This defaults to 15 days.
 
 The optional configuration variable 'gc.packrefs' determines if
-`git gc` runs `git-pack-refs`.  Without the configuration, `git-pack-refs`
-is not run in bare repositories by default, to allow older dumb-transport
-clients fetch from the repository,  but this will change in the future.
+`git gc` runs `git-pack-refs`. This can be set to "nobare" to enable
+it within all non-bare repos or it can be set to a boolean value.
+This defaults to true.
 
 The optional configuration variable 'gc.aggressiveWindow' controls how
 much time is spent optimizing the delta compression of the objects in