Updated libopenmpt to 0.2.6611.

Add pulseaudio option, default on to follow upstream.

libopenmpt 0.2-beta18 (2016-07-11)

[Change] openmpt123: Add PulseAudio output support. Autotools and
  Makefile build systems now depend on libpulse and libpulse-simple
  by default. Disable with --without-pulseaudio or NO_PULSEAUDIO=1
  respectively. When enabled, PulseAudio will be the default output
  driver,
[Change] xmp-openmpt: Settings are now stored in xmplay.ini like
  with every other plugin.
[Regression] openmpt123: Support for FLAC < 1.3.0 has been removed.
  FLAC before 1.3.0 is broken beyond repair as it provides assert.h
  in the include path.
[Bug] Generated pkg-config file libopenmpt.pc by both Makefile and
  Autotools build systems was totally broken.
[Bug] libopenmpt no longer uses the non-thread-safe global std::rand()
  function.
[Bug] Sample loops in GDM modules did not work when using Emscripten.
[Bug] XM and MO3 loaders could crash due to unaligned memory accesses.
[Bug] Fixed incorrect handling of custom MPTM tunings on big endian
  platforms.
[Bug] Fixed various problems found with clang 3.8 static analyzer,
  address sanitizer and undefined behaviour sanitizer.
[Bug] File header probing functionality was broken for most formats.
[Bug] With non-seekable streams, the entire file was almost always
  cached even if it was not of any supported module type.
  Seeking in allsubsongs-mode now works correctly.
openmpt123: Added subsong support.
Various playback fixes for 669, IT, MT2 and MTM files.
Some MOD files with more than 128 patterns (e.g. NIETNU.MOD) were
  not loaded correctly.
A new example libopenmpt_example_c_probe has been added which
  demonstrates the usage and flexibility of openmpt_could_open_propability()
  in the C API under various constraints.


(wiz)