WP 34S and 31S bugs and fixes

[Marcus von Cube]

Thanks to Bit for his detective work! I've committed the latest changes.

There is something to consider when removing functions from catalogs in integer mode: In a program they can nevertheless be entered and executed in integer mode because the mode switch and the command entry are independent. Thus, there must always be a runtime check in the command execution to prevent undesired behavior. Many commands are just dummies in integer mode as Pauli has already explained.