`magit-process-*-prompt{,s}': append '-regexp{,s}' to var names

Prevent confusion with the indentically/similarly named functions,
and make obvious which code the following commits touch.

Signed-off-by: Pieter Praet <pieter@praet.org>
`magit-process-password-prompt-regexps': support ssh(1)'s RSA key prompt

See:
  $ strings $(which ssh) | grep -i passphrase

Signed-off-by: Pieter Praet <pieter@praet.org>
Makefile: add 'test-interactively' target

Suggested-By: Pieter Praet <pieter@praet.org>
Makefile: consistently format inline elisp
Makefile: cosmetics
Merge branch 'praet/process-prompts'
magit-process-yes-or-no-prompt: cosmetics