[LITMUS^RT] crash fixes and cleanups in staging

[Björn Brandenburg]

Hi everyone,

I've extracted a couple of patches from our RTAS'14 work and pushed them to the 'staging' branch.

	https://github.com/LITMUS-RT/litmus-rt/commits/staging

Notable changes:

	- Tasks become non-real-time tasks before exiting.
	- Synchronous release support has been reimplemented yet again.
	- LITMUS^RT is the top scheduling class again.
	- Add task_cleanup() to plugin interface to enable deallocation/cleanup operations that may suspend.

The first three fix a couple of (rare) crashes that we were seeing on large multicore platforms (but hardly ever in KVM/Qemu). Please give the patches a test if you get a chance (on real hardware, if possible).

Thanks,
Björn