evaluate: relax type-checking for integer arguments in mark statements

evaluate: relax type-checking for integer arguments in mark statements

In order to be able to set ct and meta marks to values derived from
payload expressions, we need to relax the requirement that the type of
the statement argument must match that of the statement key.  Instead,
we require that the base-type of the argument is integer and that the
argument is small enough to fit.

Add one testcase for tests/py.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>