Add missing test

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Modify the parser for accepting expressions such as: 'fun a b, f a b', 'forall a, f a > 0', etc. This is just syntax sugar for 'fun (a : _) (b : _), f a b' and 'forall a : _, f a > 0'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>