Grab bag of compiler optimizations

@gkossakowski This work comes from my branch that we
went through in Lausaunne a few months back.

Sorry I was so slow to submit this as PRs. I had hoped
to find more time to robustly benchmark, but you know
how it goes...

When I tried, your benchmark tool showed the usual
problems of saying anything conclusive about individual
commits, but the trend over the entire series unambigious.
The entire series showed ~30% delta for FSC-style compilation,
~20% for SBT-style (new Global instance each compilation batch.)

I'm trying to submit what I consider to be uncontroversial
changes in groups. If a particular change requires deeper
review, I'll submit it individually.

/cc @ichoran