If we get a repo path like "-repo.git", we may try to invoke
"git-upload-pack -repo.git". This is going to fail, since
upload-pack will interpret it as a set of bogus options. But
let's reject this before we even run the sub-program, since
we would not want to allow any mischief with repo names that
actually are real command-line options.

You can still ask for such a path via git-daemon, but there's no
security problem there, because git-daemon enters the repo itself
and then passes "."  on the command line.
Signed-off-by: NJeff King <peff@peff.net>
Reviewed-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>