Always disallow the use of non-deterministic functions in CHECK constraints,

even date/time functions that use the 'now' or similar keywords.  Provide
improved error messages when this requirement is not met.
Ticket [830277d9db6c3ba1]

FossilOrigin-Name: 2978b65ebe25eeabe543b67cb266308cceb20082a4ae71565d6d083d7c08bc9f