Ticket #132 and revision r1606 updated the Windows configuration system to use PA_USE_* macros. In the process of creating the patch we decided that PA_USE_* macros should have values of 0 or 1, with pa_hostapi.h providing a defaulting mechanism.

At present Unix host apis expect PA_USE_* to be defined/undefined, not 0 or 1

Unix host APIs should be brought into line:

- pa_hostapi.h should be updated to default Unix PA_USE_* macros to 0 or 1, same as Windows macros
- pa_unix_hostapis.c should be updated to use #if instead of #ifdef for PA_USE_* macros
- any other usage of PA_USE_* macros in Unix code should be updated to take the new usage into account

The Unix build scripts should be able to remain unchanged since the new defaulting mechanism will work with the previous defined/undefined usage.