Merge branch 'tb/clone-ssh-with-colon-for-port' into maint

Remote repository URL expressed in scp-style host:path notation are
parsed more carefully (e.g. "foo/bar:baz" is local, "[::1]:/~user" asks
to connect to user's home directory on host at address ::1.

* tb/clone-ssh-with-colon-for-port:
  git_connect(): use common return point
  connect.c: refactor url parsing
  git_connect(): refactor the port handling for ssh
  git fetch: support host:/~repo
  t5500: add test cases for diag-url
  git fetch-pack: add --diag-url
  git_connect: factor out discovery of the protocol and its parts
  git_connect: remove artificial limit of a remote command
  t5601: add tests for ssh
  t5601: remove clear_ssh, refactor setup_ssh_wrapper