Merge branch 'master' into namespaced

This is a no-op merge, explicitly considering and rejecting the
submodules from the master branch.  After this merge, future merges
from the master branch will pick up any content changes.

  $ git merge --log --no-ff --strategy ours master

* master:
  shell/exercises/hearing: Replace 2012-04-uchichicago commit with 2012-02-trieste
  shell: Add a submodule with POSIX shell examples