Use full install_name for libdiffpy build on Mac OS X.

This supports linking and use of build/.../libdiffpy.dylib
from any path.
Preserve settings when replacing PQEvaluator.

PairQuantity::setEvaluatorType now preserves settings such
as useFullSum or parallel-run variables from the replaced original.
Sort distance entries by pointers.

No need to create a bunch of vectors.