In some cases Roslyn seems to emit 2 assemblies not 1 - take the last one

Right now we take the First Roslyn assembly, but we should take the last. Sometimes it emits two, and the first one is invalid  by the time second is emitted (as if it was a scripting session).

![2013-10-11_0440](https://f.cloud.github.com/assets/1710369/1311929/c637dbc6-3220-11e3-8953-1c66b71ca14a.png)

I'll check with Roslyn guys, but in the meantime this should fix #483.