remerging sigint handling....
Merge branch 'master' of github.com:pyfarm/pyfarm-agent
adding warning on Windows for missing OpenSSL library
handling empty mac addresses
Merge pull request #69 from pyfarm/small_windows_fix

handling empty mac addresses
Merge branch 'master' of github.com:pyfarm/pyfarm-agent into master_reannounce
typo fix