Achieved by adding a new element property called CarriesTypeIn, whose bits signal to save loading code which properties of particles of the element class in question carry element IDs. The bits in this property are numbered the same way as sim.FIELD_* constants for consistency. One would signal from Lua that a custom element carries element IDs in its tmp like this:
elem.property(id, "CarriesTypeIn", 2 ^ sim.FIELD_TMP)
"Carrying an element ID in a property" is to be interpreted as follows: the property is treated as a combination of a PMAPBITS-bit (so, currently 9-bit) unsigned integer lower part holding an element ID and a 32-PMAPBITS-bit (so, currently 23-bit) signed integer upper part holding whatever makes sense for the element. CONV, for example, uses this signed integer in its ctype as the extra "v" parameter for particle creation.
The rest will will in a commit soon that adds the Create event and some other stuff
Lua events will come after that
PLSM default temp lowered to MAX_TEMP
PSTN, CRAY, and possibly some others will need to be modified to account for this without breaking saves. The save format will need to include PMAPBITS and adjust properly
ACEL, changed a range check
DRAY, Fixed repetitive checking
GOLD, less rand()
PLNT, removed range checks, less rand()
PROT, used a switch()
VIBR, less rand()
VINE, less rand(), fixed growing along WOOD
VIRS, less rand()
