Merge pull request #21 from david-farrar/master

don't reap what isn't there
shutdown properly when the reactor signals an error
fix sending responses when we do not yet have the answer
Early return in options, handle missing response
Merge pull request #22 from readevalprint/fix/tim/fix_options_response

Early return in options, handle missing response
massaging of previous patch to prevent the creation/destruction of a try block
Merge branch 'master' of https://github.com/Exa-Networks/exaproxy