Functional Dependency anaylsis on lookup joins doesn't handle when key expression is an Arithmetic expression

[Nick Tobey]

Put a breakpoint in lookupJoinSelectivity before the call to sql.NewLookupFDs

Run the following SQL:

CREATE table xy (x int primary key, y int);
CREATE table uv (u int primary key, v int);
insert into xy values (1,0), (2,1), (0,2), (3,3);
insert into uv values (0,1), (1,1), (2,2), (3,2);
SELECT * FROM xy WHERE (
      				EXISTS (SELECT * FROM xy Alias1 WHERE Alias1.x = (xy.x + 1)));

As part of costing joins, we attempt to detect lookups that we know will always return at most one row. This is a perfect candidate of such a lookup: We use xy.x+1 as the key into a lookup on the primary key index Alias1.x. This always has at most one result. So we expect that fds.HasMax1Row() within lookupJoinSelectivity should return true. But it returns false instead, and we fail to prioritize this execution plan.