WyIL: Finished Updating Verifier for Assert Blocks

Assert blocks are now implemented and working for #377.  Unfortunately,
getting them to work has been something of a hack and the verifier
really needs significant reworking to account for this.  In particular,
it needs to explore blocks in a recursive fashion as per #420.
WyCS: Added test cases for #423.

These test that a contradiction is determined for when x is a strict
subset of y and vice versa.
WyCS: Partial fix for #423.

This fixes the discrepency between the use of case blocks and inline
logical OR expressions.  However, it doesn't fix the underlying problem
that these test cases should pass.