add version-checking for Cython

better warnings for users of too-old Cython.
don't turn EINTR into KeyboardInterrupt

This is redundant, and ends up doing the wrong thing when a signal handler is registered for SIGINT.
Merge pull request #336 from minrk/oldcython

add version-checking for Cython

better warnings for users of too-old Cython.

closes #335
Merge pull request #338 from minrk/sigint

don't turn EINTR into KeyboardInterrupt

This is redundant, and ends up doing the wrong thing when a signal handler is registered for SIGINT.
apply PR #338 to cython checkrc as well
add checkrc to setup.py dependencies
Added simple example for socket monitoring.
Merge remote-tracking branch 'minrk/master'