Using worker threads instead of httpd threads means that we, not libevent,
decide which requests get handled by which threads. This means that we can
make sure blocking requests (e.g. volume changes) don't get in the way of
realtime(ish) stuff like mp3 streaming.
Includes refactor of httpd_stream_file() since it was a bit of a monster.
Added various macros to check return values and log any errors and abort
if the call fails.
Updated logging to handle early errors before logging initialized.
Added a real config.rpath
Fixed build date calc for BSD
Require some needed headers at configure time
Correctly check libav functions using pkg-config flags
Made checks for some Linux features available on other ports
Fixed porting issue with antlr dep files
Added default HOST_NAME_MAX if not defined
Added missing libav header
