EDF priority tie-breaks.wip-robust-tie-break

Instead of tie-breaking by PID (which is a static
priority tie-break), we can tie-break by other
job-level-unique parameters. This is desirable
because tasks are equaly affected by tardiness
since static priority tie-breaks cause tasks
with greater PID values to experience the most
tardiness.

There are four tie-break methods:

1) Lateness.  If two jobs, J_{1,i} and J_{2,j} of
tasks T_1 and T_2, respectively, have equal
deadlines, we favor the job of the task that
had the worst lateness for jobs J_{1,i-1} and
J_{2,j-1}.

Note: Unlike tardiness, lateness may be less than
zero. This occurs when a job finishes before its
deadline.

2) Normalized Lateness.  The same as #1, except
lateness is first normalized by each task's
relative deadline.  This prevents tasks with short
relative deadlines and small execution requirements
from always losing tie-breaks.

3) Hash. The job tuple (PID, Job#) is used to
generate a hash. Hash values are then compared.
A job has ~50% chance of winning a tie-break
with respect to another job.

Note: Emperical testing shows that some jobs
can have +/- ~1.5% advantage in tie-breaks.
Linux's built-in hash function is not totally
a uniform hash.

4) PIDs. PID-based tie-break used in prior
versions of Litmus.

Conflicts:

	litmus/edf_common.c

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