This commit merges the branch arithmetic/propagation-again into trunk.

This commit merges the branch arithmetic/propagation-again into trunk.
	- This adds code for bounds refinement, and conflict weakening.
	- This adds util/boolean_simplification.h.
	- This adds a propagation manager to theory of arithmetic.
	- Propagation is disabled by default.
	- Propagation can be enabled by the command line flag "--enable-arithmetic-propagation"
	- Propagation interacts *heavily* with rewriting equalities, and will work best if the command line flag "--rewrite-arithmetic-equalities" is enabled.