Sync with 2.14.2

* maint:
  Git 2.14.2
  Git 2.13.6
  Git 2.12.5
  Git 2.11.4
  Git 2.10.5
  cvsimport: shell-quote variable used in backticks
  archimport: use safe_pipe_capture for user input
  shell: drop git-cvsserver support by default
  cvsserver: use safe_pipe_capture for `constant commands` as well
  cvsserver: use safe_pipe_capture instead of backticks
  cvsserver: move safe_pipe_capture() to the main package