Temporary workaround for issue #169

Need to reproduce this case in a unit test, either with the CLR putting
the type-cast in or with a manual type-cast, and then come up with a
more generic fix here.  Also should apply to the two-parameter lambda
converter.
Proposed correct fix and unit tests for issue #169
Merge pull request #170 from mfenniak/issue_169

Allow no-op casts in expression trees on parameters