RSR should fork incoming Commands at the framework priority

[kurtkilpela]

RsrConnection>>_receivedCommand: forks a process to handle each incoming event at the current process priority. In the process, the priority is then changed to the framework priority. Since this message is sent in the I/O process, it is forked at I/O priority and then the priority is immediately lowered. Depending upon the behavior of the ProcessorScheduler, this could result in two unnecessary process swaps.

The process should be forked at the framework priority directly.