git-gui: Assume unfound commands are known by git wrapper
git-gui: Assume unfound commands are known by git wrapper

If we cannot locate a command in $gitexecdir on our own then it may
just be because we are supposed to run it by `git $name` rather than
by `git-$name`.  Many commands are now builtins, more are likely to
go in that direction, and we may see the hardlinks in $gitexecdir go
away in future versions of git.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>
destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git