Add t/t4151-am.sh that does basic testing of git-am functionality,
including:
* am applies patch correctly
* am changes committer and keeps author
* am --signoff adds Signed-off-by: line
* am stays in branch
* am --signoff does not add Signed-off-by: line if already there
* am without --keep removes Re: and [PATCH] stuff
* am --keep really keeps the subject
* am -3 falls back to 3-way merge
* am pauses on conflict
* am --skip works
* am --resolved works
* am takes patches from a Pine mailbox
* am fails on mail without patch
* am fails on empty patch
Signed-off-by: Stephan Beyer <s-beyer@gmx.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>