First implementation of SMP parallel primitives.

Added primitives for developing multi-threaded parallel
algorithms. Include are vtkSMPTools, which currently
provides a parallel For implementation; support for simple
and initializable functors, which are needed to implement
parallel kernels and thread local storage objects that
provide storage local to each thread.

Change-Id: I4c27b25bc2dd7f0ce3194d4488864fef4444c9d3
Merge topic 'smp-parallel-framework' into master

5abad992 First implementation of SMP parallel primitives.
ENH: Update selected Filters/Core to support DesiredOutputPrecision

This updates a first batch of core filters to support a choice of
desired precision (default, single, or double) for output points. It
uses the analogous code in vtkThreshold as a model.

Change-Id: I4fadc768f1b4f5ade69445840ae8b0a8c820bc3b