This patch breaks DECL_OVERLOADED_OPERATOR_P apart into a predicate (as 
its name suggests) and DECL_OVERLOADED_OPERATOR_CODE, an accessor. I 
also add DECL_OVERLOADED_OPERATOR_IS, whose current implementation is a 
stepping stone to more a compressed operator enumeration.  Also add 
assign_op_identifier and call_op_identifier, which we use reasonably 
commonly.

I also notice that we're marking a lambda's conversion operator as an 
overloaded TYPE_EXPR.  That's weird and unnecessary, so this marks it 
simply as a conversion operator.

We're a little inconsistent in whether we check those two overloads by 
looking for identifier equivalence or examining the operator code 
enumeration.  I've not addressed that.

Applying to trunk.

nathan
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Nathan Sidwell