Here, the internal representation of &Base::method in the templates 
involves an OFFSET_REF around 'this', and we were treating the two 
instances of Wrapper as equivalent.  But they involve different 'this' 
parameters, which makes a difference when we go to look up the local 
specialization.  So we need to be stricter when comparing hash table 
entries so that they aren't shared.

Tested x86_64-pc-linux-gnu, applying to trunk, 4.7 and 4.6.