Disable `MonoOlverloadBug6541Test` for now.

Until issue #29 is closed.
Merge pull request #31 from JayBazuzi/mono6541-workaround

Disable `MonoOlverloadBug6541Test` for now.

All unit tests pass in Travis - making progress!
Merge remote-tracking branch 'jay/master' into mac
updated rakefile to run NUnit from the tools dir and use the Pash.nunit test assemblies spec