Add i18n support for scripted Porcelains, and mark strings in
merge(-recursive), am, and rebase for i18n.

* jx/i18n-1.7.11:
  i18n: merge-recursive: mark strings for translation
  Remove dead code which contains bad gettext block
  i18n: am: mark more strings for translation
  rebase: remove obsolete and unused LONG_USAGE which breaks xgettext
  i18n: Rewrite gettext messages start with dash
  i18n: rebase: mark messages for translation
  i18n: New keywords for xgettext extraction from sh