NAME:
	diffmag_byclass
 PURPOSE:
       as diffmage_wfc, spearated by class 1st rather than ccd
 CALLING SEQUENCE:
	diffmag_byclass,wfcdb,wfc_image[,ps=ps,gif=gif,col=col]
 INPUTS:
	wfcdb:The wfc database to be searched. Must start with 'dbase/... '
	wfc_image: the image 
 OPTIONAL OUTPUT KEYOWRDS:
	ps: file name of the output ps file 
	gif:root file name of the 4 output gif files. Only active if ps is 
		not set. (will have gif_all.gif, gif_stars.gif,...)
	If neither set the output is sent to an IDL graphics window
	field: STRING: name of field ie directory where the wfc/ dir is
 EXAMPLE:
	diffmag_wfc,'wfc','r219698'[,ps='diff_i_wfc']
 CALLED PROCEDURES:
	astrolib procedures,select_classes,wcs_zpn,mk_plot_diff,oplot_diff
	ops,cps,ogif,cgif,select_ccd
 MODIFICATION HISTORY:
	31-Oct-2000  Original by Suzanne Aigrain

(See /home/xmmssc/soft/idl/pro/wfcqc/diffmag_byclass.pro)