Cleanup of cross-version tests

[latkin]

Now that the compiler copies FSharp.Core.dll locally by default, the cross-version tests are passing somewhat by accident. They will fail if you run them outside of the Perl test runner - they only pass because the dummy.fs compile caused an initial copy-local that happens to make things work.

This is a small change that makes things more robust/explicit/intentional.

• Explicitly copy the desired FSharp.Core version locally before invoking the test exe
  • Ensures resolution is fully controlled for both new and old compiler versions
• Delete any local FSharp.Core copies before invoking FSI
  • Old FSI crashes on startup if FSharp.Core 4.4.0.0 is in the local directory due to "can't find sigdata/optdata" error

Also went ahead and removed 2 excluded test scenarios which now work post- F# 4.0

[latkin]

Motivation for this was problems I hit while adding some tests for the struct records PR

[KevinRansom]

Nice ... I'm glad to have you around Lincoln.

[dsyme]

Looks good, we can accept this

[dsyme]

I'll merge since it's a testing issue