Maps of Record types sometimes fail

[nickbattle]

Under some circumstances, maps that are comprised of record values of different types can cause NullPointerExceptions to be raised. The minimum test case is:

types
    P :: ;
    
    Q :: ;
    
    R :: ;
    
values
    V : map P | Q | R to nat =
    {
	mk_P() |-> 1, 
	mk_Q() |-> 2,
	mk_R() |-> 3
    };

This fails at initialization (of the V value) with a null pointer exception.

[nickbattle]

This was caused by the return value from RecordValue.compareTo when the arguments are records of different types. By returning the fixed value Integer.MIN_VALUE, it violates the compareTo contract which must return sgn(x<y) = -sgn(y<x). Changing this to user the super.compareTo fixes the bug.

[nickbattle]

Fix now in ncb/development.