clone: do not use port number as dir name

clone: do not use port number as dir name

If the URI contains a port number and the URI's path component is
empty we fail to guess a sensible directory name. E.g. cloning a
repository 'ssh://example.com:2222/' we guess a directory name
'2222' where we would want the hostname only, e.g. 'example.com'.

We need to take care to not drop trailing port-like numbers in
certain cases. E.g. when cloning a repository 'foo/bar:2222.git'
we want to guess the directory name '2222' instead of 'bar'.
Thus, we have to first check the stripped URI for path separators
and only strip port numbers if there are path separators present.
This heuristic breaks when cloning a repository 'bar:2222.git',
though.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>