update git-repack documentation wrt repack.UseDeltaBaseOffset

This default for repack.UseDeltaBaseOffset has been "true" since
Git v1.6.0.

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

Documentation/git-repack.txt

@@ -109,15 +109,15 @@ other objects in that pack they already have locally.
 Configuration
 -------------
 
-When configuration variable `repack.UseDeltaBaseOffset` is set
-for the repository, the command passes `--delta-base-offset`
-option to 'git pack-objects'; this typically results in slightly
-smaller packs, but the generated packs are incompatible with
-versions of git older than (and including) v1.4.3; do not set
-the variable in a repository that older version of git needs to
-be able to read (this includes repositories from which packs can
-be copied out over http or rsync, and people who obtained packs
-that way can try to use older git with it).
+By default, the command passes `--delta-base-offset` option to
+'git pack-objects'; this typically results in slightly smaller packs,
+but the generated packs are incompatible with versions of Git older than
+version 1.4.4. If you need to share your repository with such ancient Git
+versions, either directly or via the dumb http or rsync protocol, then you
+need to set the configuration variable `repack.UseDeltaBaseOffset` to
+"false" and repack. Access from old Git versions over the native protocol
+is unaffected by this option as the conversion is performed on the fly
+as needed in that case.
 
 
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