PrDrvrClose
PrDrvrClose closes the printer driver, allowing its code and data to be purged.
The system equate iPrDrvrRef is defined as -3 in the PrintMgr.h header
file.
This low-level function is not used by most applications. However, since
the higher-level PrClose does not actually release the memory used by the printer driver, you may wish to call this function after calling PrClose.