Alec Theriault authored Oct 04, 2018 and Ryan Scott committed Oct 04, 2018

Summary:
When converting from TH AST back to HsType, we were occasionally
dropping type arguments. This resulted in incorrectly accepted programs
as well as incorrectly rejected programs.

Test Plan: make TEST=T15360a && make TEST=T15360b

Reviewers: goldfire, bgamari, tdammers

Reviewed By: bgamari, tdammers

Subscribers: RyanGlScott, rwbarton, carter

GHC Trac Issues: #15360

Differential Revision: https://phabricator.haskell.org/D5188