Catch more exceptions on slave spawning.

As slave spawning is handled by Isolate plugins, there's no way to
predict possible exception types, so catch more stuff, just in case.
Even more exception handling on slave spawning.
Merge pull request #52 from andrusha97/master

A more reasonable default value of grow threshold.
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.
COCAINE-80: client -> app streaming, part one.

Implemented mechanics through which services could switch downstream
protocols on method invocation, for example to replace the service
protocol with a streaming protocol when a particular method is called.
Merge branch 'master' of github.com:cocaine/cocaine-core
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.
Revert a dupe.
Fixed builds on GCC 4.6 and Clang 5.0.
Check if a pointer is not null before dereferencing it.

Channel may not have attached stream. In this case footprint equals 0.