Merge branch 'ls/subtree'

Merge branch 'ls/subtree'

"git subtree" updates.

* ls/subtree: (30 commits)
  subtree: be stricter about validating flags
  subtree: push: allow specifying a local rev other than HEAD
  subtree: allow 'split' flags to be passed to 'push'
  subtree: allow --squash to be used with --rejoin
  subtree: give the docs a once-over
  subtree: have $indent actually affect indentation
  subtree: don't let debug and progress output clash
  subtree: add comments and sanity checks
  subtree: remove duplicate check
  subtree: parse revs in individual cmd_ functions
  subtree: use "^{commit}" instead of "^0"
  subtree: don't fuss with PATH
  subtree: use "$*" instead of "$@" as appropriate
  subtree: use more explicit variable names for cmdline args
  subtree: use git-sh-setup's `say`
  subtree: use `git merge-base --is-ancestor`
  subtree: drop support for git < 1.7
  subtree: more consistent error propagation
  subtree: don't have loose code outside of a function
  subtree: t7900: add porcelain tests for 'pull' and 'push'
  ...