Added support for arbitrary deadlines.

Constraint: Relative deadline must be >= exec cost.

Use: Set relative deadline in rt_task::rdeadline. Set value to 0
     to default to implicit deadlines.

Limitations: PFAIR not supported by this patch. PFAIR updated to
     reject tasks that do not have implicit deadlines.

Add a comment to explain how priorities are
interpreted, and provide some useful macros for
userspace.

Prior to that it was only used internally for DPCP

      dissertation (branch bbb-diss) to current
      version of litmus

This is needed for ongoing projects

I took the unchanged code but removed some leftovers
of OMLP which is not implemented

This patch changes how preemptions of jobs without
budget work. Instead of requeuing them, they are now
only added if they are not subject to budget enforcement
or if they have non-zero budget. This allows us to process
job completions that race with preemptions.

This appears to fix a BUG in budget.c:65 reported by Giovani Gracioli.

litmus.h is accumulating too many things. Since
we already have budget.h, let's stick all budget-related
inline functions there as well.

This patch is merely cosmetic; it does not change
how budget enforcement works.

An efficient binary heap implementation coded in the
style of Linux's list.  This binary heap should be able
to replace any partially sorted priority queue based
upon Linux's list.

Enable kernel-style events (tracepoint) for Litmus. Litmus events
trace the same functions as the sched_trace_XXX(), but can be
enabled independently.

So, why another tracing infrastructure then:
- Litmus tracepoints can be recorded and analyzed together (single
  time reference) with all other kernel tracing events (e.g.,
  sched:sched_switch, etc.). It's easier to correlate the effects
  of kernel events on litmus tasks.

- It enables a quick way to visualize and process schedule traces
  using trace-cmd utility and kernelshark visualizer.
  Kernelshark lacks unit-trace's schedule-correctness checks, but
  it enables a fast view of schedule traces and it has several
  filtering options (for all kernel events, not only Litmus').

Increment a processor-local counter whenever an interrupt is handled.
This allows Feather-Trace to include a (truncated) counter and a flag
to report interference from interrupts. This could be used to filter
samples that were disturbed by interrupts.