We know that the version subcommand of git is special. It does not
currently have an executable link installed into $gitexecdir and we
therefore would never match it with one of our file exists tests.
So we forward any invocations to it directly to the git wrapper, as
it is a builtin within that executable.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>