update netty 4 version; close channel before waiting for the closing to finish
don't use pooled buffers in netty-websocket-transmitter
implement keep-alive in netty-websocket-transmitter
bugfix: multiple listeners were registered when elements were moved between ObservableLists
bugfix: added a way to ensure only one listener is added to a property at the whole time
- before, multiple listeners could be added under certain circumstances
- added new test to ensure the correctness of the listeners
Merge remote-tracking branch 'michael/bugfix_multiple_listeners'
deduplicate some test code