Support addresses with ':' in git-daemon

Support addresses with ':' in git-daemon

If host address could have ':' in it (e.g. numeric IPv6 address), then
host and port could not be uniquely parsed. Fix this by parsing the
"["<host>"]":<port> and "["<host>"]" notations. Currently the built-in
git:// client would send <host>:<port> or <host> for such thing, but
it doesn't matter as due to bugs, resolving address fails if <host>
contains ':'.

Signed-off-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>