Endianness fun is not provided by the same header file on GNU/Linux (endian.h) and FreeBSD (sys/endian.h). Add some magic for the autotools to detect the correct header file. While here, add AC_C_INLINE: it's reported as missing by autoscan(1).
- Changed mad_get_aid() and mad_set_aid() ABI; - Update unit test;
- Fix includes (use '<>' instead of '""'); - Add -I. to cc arguments.