PERF: Revert Remove large foot print of PDF derivatives.

This reverts commit 4c98ab6355ef578a4bfc66879e88d5467bbcc698.
The previous attempt to address speed issues resulted in
a serious performance penalty for BSpline registration types
due to the size of the derivatives generated.

Lessons learned from investigating this path are are
incorporated into the next set of patches.

Change-Id: I91f5a0efc2025efd37c9861567a2ced46dc13bc8
PERF: Distribute initialization per thread buffers

The process of zero'ing out and creating new buffers
across 32 threads is quite time consuming.  By
distributing the load across each of the threads, this can
occur in parallel, thus providing a huge speed increase.

This solution scales to many cores better than alternative
solutions attempted.

Change-Id: If1d15b6ed2045f75fa205dee21bdc3fb2714870a