add warning about fltk 1.1.7

fix cygwin compile

rewrite

moved most OS-dependent functions in OS.cpp

Cygwin is GONE!

- usleep takes microseconds
- work on c solver interf

"pure windows" version (without cygwin) is almost there: the solver
interface now works quite nicely using native Windodiows sockets and
the timers work too. There are still some bugs with binary files and
user-created functions in the parser.

replaced poll() with direct call to select(). This should help in getting
the solver interface eventually work on Windows without cygwin