MERGED: Do not combine dictionaries in the EvVarCache when simplEqsOnly is on

commit f002a461
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date:   Tue Jan 17 12:15:26 2012 +0000

Do not combine dictionaries in the EvVarCache when simplEqsOnly is on

This fixes Trac #5776; the background is in
Note [Simplifying RULE lhs constraints] in TcSimplify