Do not process messages in a dead channel.

Stop processing messages in the decoder, if it was destroyed while
processing a message in the same readable stream event iteration.
Changelog update.
Merge branch 'master' of github.com:cocaine/cocaine-core
COCAINE-80: client -> app streaming, part two.

1) Properly handle synchronous downstream destruction.
2) Set the prototype name on the derived dispatches, instead of calling
them "void" without any meaning or context.