"git p4" update.

* am/p4-branches-excludes:
  git-p4: respect excluded paths when detecting branches
  git-p4: add failing test for "git-p4: respect excluded paths when detecting branches"
  git-p4: don't exclude other files with same prefix
  git-p4: add failing test for "don't exclude other files with same prefix"
  git-p4: don't groom exclude path list on every commit
  git-p4: match branches case insensitively if configured
  git-p4: add failing test for "git-p4: match branches case insensitively if configured"
  git-p4: detect/prevent infinite loop in gitCommitByP4Change()