Subroutine:	IRCO_PRNUMBER.

 Purpose: 	Return number of plate projection system 'name'.

 File: 	irco_project.shl.

 Author:	90 Apr 25 Sjag Steensma.

 Use:	<int> = IRCO_PRNUMBER (
		prname   I	character * (*)
		)
	<int>	(function result) number (1..10) of plate
		projection system.
	prname	Name of plate projection system. Should at least
		contain idlen characters.
 Description:
	Returns number of plate projection system by comparing first
	idlen characters of prname to those, for every number, given
	by function IRCO_PRNAME.
	If prname is unknown or prname contains less than idlen characters,
	0 is returned.
 Externals:
	IRCO_PRNAME.
 Updates: