enable support for using the system portaudio library. The latter
also corrects a long standing bug that prevented using config.status
to regenerate src/Makefile.
As a result of the above, I've taken Benjamin's *_LOCAL_CONFIGURE_ARGS
idea and propagated its usage to the other place where ac_configure_args
was being set directly.
Removed old stuff from lib-src/Makefile.in and made the library locations
for portaudio and portmixer like the rest (a symlink in lib-src).
Reworked portmixer's configure.ac to properly detect host apis.
Also, in some research I learned that the DirectSound guid to Wave ID function can sometimes return success without writing to the output struct at all. I added a check to initialize and bail if this happens. This can possibly help with some of our USB issues.
note that this change may require a solution clean and rebuild because it is in libsrc.
Also affects bug 29, as before portmixer was fetching the wrong mixer when many devices were available, but this does not address all issues.
