Auto-CPU-affinity from part./cluster assignment.

This patch replaces be_migrate_to() with several
be_migrate_*() APIs to automatically assign CPU affinity
masks from a task's partition (or cluster) assignment.
Routines are release-master-aware such that the release
master (if one exists) will NOT be included in the
task's affinity mask. (Note that release-master
avoidance may be overridden by calling
__be_migrate_thread_to_cluster().)
Cluster-aware rtspin and rt_launch.

This patch adds cluster scheduling options to
rtspin and rt_launch. The convenience routines
in litmus.h were also updated to facilitate
clustered scheduling. For partitioned scheduling,
just set cluster_size = 1 (default size for rtspin
and rt_launch).
Add init_rt_task_param().

Adds init_rt_task_param(). Facilitates setting up default
real-time task attributes that cannot be set by memset(0).
Change convenience API routines.

The sproadic_*() macros have become unwieldy. This patch
replaces those convenience macros for global, clustered,
and partitioned scheduling. A part of this API change
is the explicit use of nanosecond time-values. Prior APIs
have used lt_t (litmus time), which had an implied time
scale of nanoseconds.

/bin apps and test suite also updated to use revised API.
Modifications to the test suite are mostly centered around
using nanoseconds instead of milliseconds.
Fix compile failure related to aliasing (gcc 4.4.5)

My version of gcc would complain about "dereferencing pointer does
break strict-aliasing rules" because of a (harmless) pointer cast.

This patch adds a helper void pointer to make the assignment explicit,
which avoids the cast and hence silences the warning.