[PATCH] Sema: Subst type default template args earlier

[Richard Smith]

  Can you check whether this fixes PR16689 and PR16975 too, and if so, add tests for them?

  Otherwise, LGTM. Thanks!

http://llvm-reviews.chandlerc.com/D1507

BRANCH
  DefaultTemplateArgsInst

ARCANIST PROJECT
  clang