Fix exception on hangedup streams in 2.6
take twitter's keepalive signals into account for the timeout
yield None as well in timeout mode when no tweet received
hangup should happen also in noblock mode
fix python2.6 compat and refacto per as @Adonoho's #201
use non timeout mode for all streams in the sample tester
revert to regular no yield in timeout mode until further non-blocking+timeout option
please @adonoho
Merge pull request #203 from RouxRC/pr-fix-timeout

Fix streams timeout & hangup behavior + ensure python2.6 compat
Here are the changes to fix the misbehavior of the timeout in case of low tweets by catching Twitter's keep-alive heartbeat signals thanks to the select.select originally added in #178 and still problematic as pointed out by @ksecrist in #202

I also generalized the hangup to all cases since there is no reason to stay in infinite loop after a hangup in non-blocking mode. 

And to make things easier and avoid merging issues, I adapted the refacto and fixed python2.6 compatibility from @adonoho's #201