Adding support for Consistency Assertions

[sidprasad]

Adding support for two new assertions:

assert [EXP] is consistent with [PRED] which ensures that [EXP] && [PRED] is satisfiable
assert [EXP] is inconsistent with [PRED] which ensures that [EXP] && [PRED] is unsatisfiable

Also modifying existing assertions of necessity and sufficiency to support the following:
assert [EXP] is sufficient for [PRED]
assert [EXP] is necessary for [PRED]