Update test names to use _ instead of - for newer Nunit, and use MD5 for hashing.

This commit makes the nunit tests work with versions of nunit that do not support - in the test name. Also, one instance of GetHashCode is replaced with MD5 instead to make the test work more reliably since GetHashCode is not always the same value based on the C# runtime used.  Joel Mewton and I talked about this via email on 11/07/12.