Merge branch 't/ao_fixes'

Merge branch 't/ao_fixes'

Cooking since 2014-03-22.

* t/ao_fixes:
  ao_write: Call ao_initialize() only once.
  ao_write: Join threads before returning an error from aow_post_select().
  ao_write: Simplify locking.
  Don't unlock and lock the thread mutex unnecessarily.
  ao_write: Check return value of pthread functions.
  ao_write: Avoid segfault on exit.
  ao_write: Avoid pthread_join().
  ao_write: Enforce a 20ms timeout.
  ao_write: Fix spurious segfault.