Copied a bit of code from FSharpLex.Tests to FSharpYacc.Tests to allow specific test cases to be ignored by adding an empty file with the same filename as the test case plus the '.ignore' suffix.
Added an .ignore file for a failing fsharpyacc test case. Note -- fsharpyacc is actually doing the right thing, because the specification file is ill-formed, but the code we have now to run the test cases doesn't have a way to specify that a test is expected to fail.