Allow binary-compatible indices to be considered when checking for valid

Allow binary-compatible indices to be considered when checking for valid
 indices for restriction clauses containing a constant.
Note that if an index does not match directly (usually because the types
 on both side of the clause don't match), and if a binary-compatible index
 is identified, then the operator function will be replaced by a new
 one. Should not be a problem, but be sure that if types are listed as
 being binary compatible (in parse_coerce.h) then the comparison functions
 are also binary-compatible, giving equivalent results.