Allow early initialization of classes if they don't have any [sp]init methods
We were being too conservative in determining whether to use
the static property cache when accessing a property from outside the
class. In fact we'd never use it in that case, because we required
that the class not need initialization (and any class with static
properties needs initialization!).
We can relax this restriction to just enforce that the class not
define sinit or pinit methods -- scalar properties are fine.