Added a few more global variable opcodes.
Gotta catch em all!
PRIVATE_IF_DIRECT_GLOBAL and ASSIGN_PRIVATE_IF_DIRECT_GLOBAL
These will fetch or assign a global variable if the currently
executing program is the program the object is cloned from.
These are only slightly slower than the F_PRIVATE_GLOBAL family of
opcodes, and the overhead if the global is not actually private is
Missing: [ASSIGN_]PRIVATE_IF_DIRECT_TYPED_GLOBAL[_AND_POP] and