Use NaiveFunext for proving funext_downward_closed

The new version of @mattam82's universe polymorphism isn't as libral
with inductive universes.  So we use NaiveFunext to allow a simpler
transformation of universes.

This is in preparation for switching to Coq trunk, once enough bugs are
fixed.
Merge pull request #391 from JasonGross/funext-down-naive

Use NaiveFunext for proving funext_downward_closed
Fixups to work with the latest polyproj branch.
Progress on adapting HoTT and categories to latest polyproj branch.
Progress on adapting HoTT and categories to latest polyproj branch.
Adapt categories and hit's code to latest polyproj (Private keyword).
- A few places raise universe inconsistencies in Categories still, not sure why.
- Some minor unification problems with apply/eauto discovered as well.
- Some places requiring more instances of Funext, as I expected.
Everything compiles quickly here.
Update submodule
Fix up some transparency issues
Remove an admit
More fixes
More minor changes
Remove more admits, add more work-arounds
Add back a space to minimize diff against master
Fix [simpl] going through abstract
[destruct] seems to not be working well...
Track Matthieu's trunk-polyproj branch
Update install with new branch
Workaround some bugs with new trunk-polyproj branch
Fixups to work with the latest polyproj branch.
Adapt categories and hit's code to latest polyproj (Private keyword).
- A few places raise universe inconsistencies in Categories still, not sure why.
- Some minor unification problems with apply/eauto discovered as well.
- Some places requiring more instances of Funext, as I expected.
Everything compiles quickly here.