bindingConstraints1 does not detect support non-metavariable constraints

[nathancarter]

• If we have for.all[x,equ.als(x,y)] with all variables marked as metavariables, then bindingConstraints1 correctly yields the pair (y,x).
• If we have the same pattern but with only the xs marked as metavariables, then bindingConstraints1 yields no pairs. Consequently, it would think that it was acceptable for that pattern to match for.all[y,equ.als(y,y)], whereas there is actually variable capture in that case.