Make QtScript use strict type checking when invoking a slot

QtScript will allow a function to be called even if the type passed in doesn't match the one the function has a parameter. For example, a function can have an int parameter but it will also accept a string to be passed in.

Due to the dynamic typing of QtScript, passing a string to a slot that takes an int is allowed. However, in a future release we may introduce a mode that tells QtScript to perform strict type checking.