Add regression tests for univ. poly. and prim proj

These regression tests are aggregated from the various bugs I (and
others) have reported on https://github.com/HoTT/coq/issues relating to
universe polymorphism, primitive projections, and eta for records.
These are the tests that trunk currently passes.

I'm not sure about the naming scheme (HoTT_coq_###.v, where ### is the
number of the issue in GitHub), but I couldn't think of a better one.