rwbarton authored Apr 06, 2017 and Ben Gamari committed Apr 06, 2017

Part of e13419c5 was accidentally lost during a rebase. This commit
adds the missing change, along with some more improvements
regarding where we do and don't use `seqType`.

Also include a comment about where the space leak showed up
and a Note explaining the strategy being used here.

Test Plan: harbormaster, plus local testing on DynFlags

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D3421