Merge branch 'jn/ssh-wrappers'

Merge branch 'jn/ssh-wrappers'

The ssh-variant 'simple' introduced earlier broke existing
installations by not passing --port/-4/-6 and not diagnosing an
attempt to pass these as an error.  Instead, default to
automatically detect how compatible the GIT_SSH/GIT_SSH_COMMAND is
to OpenSSH convention and then error out an invocation to make it
easier to diagnose connection errors.

* jn/ssh-wrappers:
  connect: correct style of C-style comment
  ssh: 'simple' variant does not support --port
  ssh: 'simple' variant does not support -4/-6
  ssh: 'auto' variant to select between 'ssh' and 'simple'
  connect: split ssh option computation to its own function
  connect: split ssh command line options into separate function
  connect: split git:// setup into a separate function
  connect: move no_fork fallback to git_tcp_connect
  ssh test: make copy_ssh_wrapper_as clean up after itself