Merge branch 'pb/am-show-current-patch'

Merge branch 'pb/am-show-current-patch'

"git am --short-current-patch" is a way to show the piece of e-mail
for the stopped step, which is not suitable to directly feed "git
apply" (it is designed to be a good "git am" input).  It learned a
new option to show only the patch part.

* pb/am-show-current-patch:
  am: support --show-current-patch=diff to retrieve .git/rebase-apply/patch
  am: support --show-current-patch=raw as a synonym for--show-current-patch
  am: convert "resume" variable to a struct
  parse-options: convert "command mode" to a flag
  parse-options: add testcases for OPT_CMDMODE()