The driver id returned by libao wasn't checked correctly.
When the driver did not exist, libao returns a negative number. The
libao output driver checked for a non zero id.
This caused shairport to refuse to use the first driver, and not fail
when using a non-existant driver.
Perl script is removed in favour of C. Stale documentation and initfiles
are removed for now also.
C interface works, but still needs work (for example, mDNS is missing) -
see TODO.