Fixed build on OSX.

- For some reason the "extern int pid_daemon" usage in libwebsockets.c would cause an "undefined symbols" linker error for the test-apps. This only happens with the CMake project, not the normal Makefiles. I have no clue why this is. Fixed it by getting the pid via a function instead.

- Added test-server-extpoll

- Renamed the library from libwebsocket -> libwebsockets