Merge branch 'pt/am-builtin'

Merge branch 'pt/am-builtin'

Rewrite "am" in "C".

* pt/am-builtin: (46 commits)
  git-am: add am.threeWay config variable
  builtin-am: remove redirection to git-am.sh
  builtin-am: check for valid committer ident
  builtin-am: implement legacy -b/--binary option
  builtin-am: implement -i/--interactive
  builtin-am: support and auto-detect mercurial patches
  builtin-am: support and auto-detect StGit series files
  builtin-am: support and auto-detect StGit patches
  builtin-am: rerere support
  builtin-am: invoke post-applypatch hook
  builtin-am: invoke pre-applypatch hook
  builtin-am: invoke applypatch-msg hook
  builtin-am: support automatic notes copying
  builtin-am: invoke post-rewrite hook
  builtin-am: implement -S/--gpg-sign, commit.gpgsign
  builtin-am: implement --committer-date-is-author-date
  builtin-am: implement --ignore-date
  builtin-am: pass git-apply's options to git-apply
  builtin-am: implement --[no-]scissors
  builtin-am: support --keep-cr, am.keepcr
  ...