connect.c: allow ssh://user@[2001:db8::1]/repo.git

connect.c: allow ssh://user@[2001:db8::1]/repo.git

The ssh:// syntax was added in 2386d658 (Add first cut at "git
protocol" connect logic., 2005-07-13), it accepted
ssh://user@2001:db8::1/repo.git, which is now legacy.

Over the years the parser was improved to support [] and port numbers,
but the combination of ssh://user@[2001:db8::1]:222/repo.git did
never work.

The only only way to use a user name, a literall IPV6 address and a port
number was ssh://[user@2001:db8::1]:222/repo.git

(Thanks to Christian Taube <lists@hcf.yourweb.de> for reporting this long
standing issue)

New users would use ssh://user@[2001:db8::1]:222/repo.git,
so change the parser to handle it correctly.

Support the old legacy URLs as well, to be backwards compatible,
and avoid regressions for users which upgrade an existing installation
to a later Git version.

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>