plxormod: Enter or leave xor mode

plxormod (mode, status);

Enter (mode !=0) or leave (mode == 0) xor mode for those drivers (e.g., the xwin driver) that support it. Enables erasing plots by drawing twice the same line, symbol, etc. If driver is not capable of xor operation returns status of 0.

mode (PLINT, input)

mode != 0 means enter xor mode and mode == 0 means leave xor mode.

status (PLINT *, output)

Pointer to status. Returned status == 1 (0) means driver is capable (incapable) of xor mode.