This patch creates a new character device, uncachedev.
Pages of RAM allocated by this device are not cached by
CPUs.

Uses for such pages:
1) Determining *very* pessimistic emperical worst-
   case execution times.
2) Compare against performance with caches (quantify
   the avg. case benefit).
3) Deterministic memory accesses (access cannot cause a
   cache eviction.)
4) Theoretically, increased performance can be achieved
   by storing infrequently accessed data in uncache pages.

uncachedev allocates pages with the pgprot_noncached() page
attribute for user applications. Since pages allocated by
uncachedev are not locked in memory by default, applications
with any access level may mmap pages with uncachedev.

Limitations:
1) Uncache pages must be MAP_PRIVATE.
2) Remapping not supported.

Usage (user level):
	int size = NR_PAGES*PAGE_SIZE;
	int fd = open("/dev/litmus/uncache", O_RDWR);
	char *data = mmap(NULL, size, PROT_READ | PROT_WRITE,
					MAP_PRIVATE, fd, 0);
	<...do stuff...>
	munmap(data, size);

If a task is released on a CPU that is idle, then it is pointless to
send an IPI to another CPU just to schedule the newly released task.
This patch changes check_for_preemptions() to prefer the local CPU
first if it is idle.

Assigning a nice value to LITMUS^RT tasks is meaningless. Bail out
early.

This patch fixes a BUG_ON() in litmus/preempt.c:33 reported by Felipe
Cerqueira & Manohar Vanga.