Makes the two VSprites head and tail of the gel list that is connected to the GelsInfo structure. The two VSprites are linked together and their x and y coordinates are initilized such that the serve as the keystones of the list.
INPUTS
head
pointer to the VSprite structure to be used as head of the gel list
tail
pointer to the VSprite structure to be used as tail of the gel list
GInfo
pointer to the GelsInfo structure to be initilized