TEMPORARY BUILD FIX

* Temporary upper limit until test-framework-quickcheck2 allows QC 2.6 (otherwise, accelerate-examples falls over)
* The latest HP ships with QC 2.6.
Revert "TEMPORARY BUILD FIX"

This reverts commit a76d1cb57985984d1f44b56a4bdb9ca13b5cbb08.
require base-4.6 (ghc-7.6)