search for: __bswap_16

Two simple patches which make libnbd compile on FreeBSD. Are we OK to copy common/include/byte-swapping.h from nbdkit? There is no license issue that I know of. Should we put it in lib/ or create a common/ directory? The header file is actually also needed by the tests (follow up patch for that) so putting it in common/ might make more sense. Some notes if you want to compile on FreeBSD: -

With these patches, a majority of tests pass. The notable things which are still broken: - Because FreeBSD links /home -> /usr/home, $(pwd) gives a different result from realpath(2). Therefore some tests which implicitly rely on (eg) a plugin which calls nbdkit_realpath internally and then checking that path against $(pwd) fail. - Shebangs (#!) don't seem to work the same way

This is an incomplete port to Windows. Currently the server compiles and starts up successfully, but goes into an infinite loop when you connect to it. Nevertheless I think the approach is ready for feedback. This being Windows the changes go quite deep. Rich.