Merge branch 'master' of git://github.com/psionides/git-subtree

* 'master' of git://github.com/psionides/git-subtree:
  improved rev_is_descendant_of_branch() function
  added temporary test dirs to gitignore
  added tests for recent changes
  fixed bug in commit message for split
  changed alias for --prefix from -p to -P
  fix for subtree split not finding proper base for new commits
  allow using --branch with existing branches if it makes sense
  added -m/--message option for setting merge commit message
  added -p alias for --prefix