* Big clean-up to allow compiling every module as plugins.
 * Added bytes_swap.h to provide ntoh() and htol() on Win32. With this
     change we don't have to link winsock2 with every plugin anymore. This
     should also give us a slight speed increase.
 * Added #define WIN32_LEAN_AND_MEAN in threads.h to speed-up compilation
     on Win32.
 * Modified ac_downmix_3dn and sse so they compile with the latest gcc for
     Win32.

(PS: the dvdread plugin doesn't compile yet on Win32)