Script: some speed optimization

Returned back to original way the script instance made its own copy of byte-code array. Thus global variables are no longer being b-searched during script execution. Also no more instruction fixup at runtime.

A small runtime fixup for consecutive PUSHREG/POPREG instructions that performs operation practically identical to REGTOREG instead of two stack operations.

As suggested by rofl0r, the search for managed object handle by given address is done in reverse order.
The experiments show that in most cases the location of the matching address is much closer to the end of array, therefore, in modern AGS games this changes saves >1000 iterations per lookup.