Merge branch 'jk/clone-progress-to-stderr' into maint

"git clone" gave some progress messages to the standard output, not to
the standard error, and did not allow suppressing them with the
"--no-progress" option.

* jk/clone-progress-to-stderr:
  clone: always set transport options
  clone: treat "checking connectivity" like other progress
  clone: send diagnostic messages to stderr