Support of multiple threads in service manager.

Now service manager can run more than one thread. Single connection is handled only by single thread, but several connections will work faster on multiprocessor systems.
Fix segfault in service_t and custom name of threads.

* service_t first resets pointer to connection and then derefernces it.
* Threads created by service manager now have name "service-manager".
Merge branch 'multithreading' into v0.11
Update changelog.