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.

diff --cc NEWS
index 4da5690551bdffb5a860316fadc4c0effc61512c,ab53a17697ea7c92f2d0b2107d4d8dcee95d9e4c..642c1fc422225141a1fa1a555113746a69b8a93e
--- 1/NEWS
--- 2/NEWS
+++ b/NEWS
@@@ -1,17 -1,9 +1,19 @@@
  NEWS
  ====
  
 ----------------------------------------------
 -0.5.2 (to be announced) "orthogonal interior"
 ----------------------------------------------
 +-------------------------------------------------
 +0.5.3 (to be released) "symbolic synchronization"
 +-------------------------------------------------
 +
 +      - Various alsa-related fixes, mostly for the raspberry pi.
 +      - The test suite has been extended to include sanity checks
 +        for the generated man pages.
++      - ao_writer fixes. This writer was in a quite bad shape. Many
++        serious bugs have been fixed.
 +
 +----------------------------------------
 +0.5.2 (2014-04-11) "orthogonal interior"
 +----------------------------------------
  
  The new sync filter, the AES_CTR128 stream cipher and the overhauled
  network code are the highlights of this release. It also includes a