Subroutine:   IRCO_NUMBER
 
 Purpose:      returns the number of a coordinate system
 
 Category	WORLD COORDINATES, IRAS

 File:         irco.shl
 
 Author:       Do Kester
 
 Person resp.: Do Kester
 
 Address:      guspace!do or rugfx4!do         (uucp)
 
 Use: integer irco_number(
 	name,    I      character*(*)
	epoch )	 I	real

	IRCO_NUMBER 	the number of the coordinate system
			negative if the name corresponds while a
			epoch can not be found
			0: system is not known
	name		the name of the system
	epoch		epoch of the system if applicable

 Description:  
 	For the system with NAME and EPOCH the coordinate number 
	is returned. EPOCH is disregarded for systems other than
	EQUATORIAL, ECLIPTIC or SUN REFERENCED. In the latter case
	epoch will be the ecliptic longitude of the sun.

	Sunreferenced with epoch 0.0 will always return the standard
	SR system. 

	For systems with an unknown epoch, the routine will try to 
	return the negative number of a system with the same name.

	Unknown systems will return a zero

 Updates:      17 July 1990 DK
		12 Sep 1990  DK add EPOCH to the calling sequence
		22 Nov 1990  DK corrected real comparison of epochs
		26 Nov 1990  DK correction in comparison of names
		11 Dec 1990  DK negative numbers