Improved implementation of WritableValue::typedPPtr()
Improved implementation of WritableValue::typedPPtr()

Non-const typedPPtr casting should not be limited to the content type of
the WritableValue value, but should also allow pointer-assignable types.

databricxx/databricxx,databricxx/databricxx,aguetlein/databricxx,aguetlein/databricxx,oschulz/databricxx,oschulz/databricxx