Fix some compiler warnings!

* The uinet bits in libev code use pthreads, but pthreads.h isn't included.
* assert() doesn't take a string - it takes a true/false value.
  So, create a macro for it and use it everywhere.
Migrate this into the right place.
Merge pull request #17 from erikarn/adrian_libev

Fix some compiler warnings!
Merge branch 'master' into passive_receive_pcap_adrian