thomasw authored Jul 03, 2015 and Ben Gamari committed Jul 03, 2015

Look through nested foralls when checking the validity of a partial type
signature. The combination of D836 and D613 prompts this change.

Test Plan: The test T10519 must pass

Reviewers: simonpj, alanz, austin

Reviewed By: simonpj, alanz, austin

Subscribers: thomie, bgamari

Differential Revision: https://phabricator.haskell.org/D994

GHC Trac Issues: #10519