Issue #727: Don't add .hs-boot modules to context

[lukemaurer]

withInteractiveContext was adding the whole module graph to the interactive context - including .hs-boot modules. This caused each symbol from any .hs-boot to be loaded twice. The .hs-boot files are of no use to us anyway, so this patch filters them out.

[DanielG]

I'd be curious to know how ghci handles this. I had a quick look yesterday and I couldn't find any sort of hs-boot specific code before they call setContext there at all.