Incorporate patches from fink to enable libao to work properly on OS X.

It still requires dlcompat, but now plugins have their own LDFLAGS variable
which is platform dependent.  Also disabled aRts by default on OS X because
it just hangs mysteriously.  macosx native plugin builds and installs but
libao can't seem to load it.  Not sure why yet.  ESD output works with
fink, however.


git-svn-id: http://svn.xiph.org/trunk/ao@4126 0101bb08-14d6-0310-b084-bc0e0c8e3800