Merge branch 'mt/p4-parse-G-output'

Use "p4 -G" to make "p4 changes" output more Python-friendly
to parse.

* mt/p4-parse-G-output:
  git-p4: filter for {'code':'info'} in p4CmdList
  git-p4: parse marshal output "p4 -G" in p4 changes
  git-p4: git-p4 tests with p4 triggers