#4673 binomial(a,a-b) doesn't simplify to binomial(a,b)

[Barton Willis]

Arguably this is a feature request, not a bug. But the binomial coefficients are so important, I'll call it a bug:

Doesn't simplify to zero

(%i255) binomial(a,a-b)-binomial(a,b);
(%o255) binomial(a,a-b)-binomial(a,b)

But makegamma takes care of it:

(%i256) makegamma(%);
(%o256) 0

[RoyalX]

makefact can handle it, too