Merge branch 't/osx_writer_improvements'

Cooking since 2012-10-30.

	9eaa22 osx_write: Check return value of AudioOutputUnitStart().
	831db3 osx_write: Be careful when dereferencing the private_data pointer.
	97902a osx: Treat writer node as an internal buffer tree node.
	1c6fa9 osx_write: Add big fat comment on callback btr node.

diff --cc NEWS
index 2c05b8f90be044f7070ef5a2a08a589e4d46b58d,6ee5086a41f3abd4b406448be51d459af9717cec..69372cc42c4ea40712fe6f5a337840875ddff04b
--- 1/NEWS
--- 2/NEWS
+++ b/NEWS
@@@ -7,7 -7,6 +7,8 @@@
          in the new "releases" branch.
        - Overhaul of the build system: All generated files are now
          written to the "build" directory.
 +      - The modular mixer API and the alsa mixer.
++      - Minor fixes for the osx writer.
  
  --------------------------------------
  0.4.11 (2012-07-20) "mutual diversity"