Merge branch 'pt/am-foreign'

Various enhancements around "git am" reading patches generated by
foreign SCM.

* pt/am-foreign:
  am: teach mercurial patch parser how to read from stdin
  am: use gmtime() to parse mercurial patch date
  t4150: test applying StGit series
  am: teach StGit patch parser how to read from stdin
  t4150: test applying StGit patch

diff --cc git-am.sh
Simple merge

diff --cc t/t4150-am.sh
Simple merge