roll INTBASIC.SYSTEM to 4ba42d9

4ba42d9 LOAD/RUN now don't clear if file doesn't exist. Saves 12 bytes.
9b65ada Reuse some RTS ops. Saves 4 bytes.
4021f74 Add LOCK/UNLOCK commands. Costs 55 bytes.
8a4b6e3 Show lock sigil in CAT/CATALOG. Costs 10 bytes.
138367c Centralize setting ref_nums after OPEN. Saves 25 bytes.
e5092c6 Eliminate need for commands to call FinishCommand. Saves 17 bytes.
cefb24a Re-use MLI calls/params and other refactoring. Saves 33 bytes
7f1e3d7 Invoke commands with ProDOS ZP swapped in. Saves 16 bytes.