Adding proper error reporting for CompilerLoader.

This hopefully eliminates an entire category of stupid crashes.
Also updating LoaderGenerator comments describing generated code, as they
were pretty out-of-date.
Adding tests around enforcing/suppressing orphan analysis of sets
Deduplicating Injects entries

It's valid for more than one module to declare the same type as an Injects
entry-point.
Promoting Trie repr from byte array to ushort array

Already hit the too-many-rows limit for bytes... oh well.
Propagating library-ness of set binding contributions.

The way this works is basically (but not actually):

IsLibrary = contributors.All(c => c.IsLibrary)
Already forgot what these flags are, so I added a comment.
Merge pull request #30 from benjamin-bader/sets-and-libraries

Sets and libraries