builtin-am: pass git-apply's options to git-apply

builtin-am: pass git-apply's options to git-apply

git-am.sh recognizes some of git-apply's options, and would pass them to
git-apply:

* --whitespace, since 8c31cb8 (git-am: --whitespace=x option.,
  2006-02-28)

* -C, since 67dad68 (add -C[NUM] to git-am, 2007-02-08)

* -p, since 2092a1f (Teach git-am to pass -p option down to git-apply,
  2007-02-11)

* --directory, since b47dfe9 (git-am: add --directory=<dir> option,
  2009-01-11)

* --reject, since b80da42 (git-am: implement --reject option passed to
  git-apply, 2009-01-23)

* --ignore-space-change, --ignore-whitespace, since 86c91f9 (git apply:
  option to ignore whitespace differences, 2009-08-04)

* --exclude, since 77e9e49 (am: pass exclude down to apply, 2011-08-03)

* --include, since 58725ef (am: support --include option, 2012-03-28)

* --reject, since b80da42 (git-am: implement --reject option passed to
  git-apply, 2009-01-23)

Re-implement support for these options in builtin/am.c.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>