Main: Improve error message
Respect ghc -osuf / -hisuf flags.

This makes profiling builds actually work.
If an -optP-include is passed, unconditionally depend on it.

BuildPlan: Allow specifying unconditional dependencies for this.
Print why a file is being (re)compiled, like newer GHCs
Main: Add final ghc --make pass. Accounts for #9
Merge pull request #12 from nh2/nh2fixes

A few more correctness fixes