Return Deferred from WampServerProtocol.dispatch()

To match the return value of WampServerFactory.dispatch()
Fix typos
Print exceptions in pubsub topic handlers instead of ignoring them
add symmetric RPC example
Merge pull request #129 from flyser/bugfix1

Return Deferred from WampServerProtocol.dispatch()
Merge pull request #130 from flyser/bugfix2

Print exceptions in pubsub topic handlers instead of ignoring them
add Flash policy file server and example for WS fallbacks
Merge branch 'master' of github.com:tavendo/AutobahnPython
Merge branch 'master' into prefixsubscribe