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 <spearce@spearce.org>