NAME:
	select_cond
 PURPOSE:
       select object which are satisfy 'cond' in all input vectors. 
	Returns a list of indexes where this is satisfied 
	and out1=in1(where(cl_vect=class)) 
 CALLING SEQUENCE:
	select_cond(cond,in1[,out1,in2,out2,in3,ou3])
 INPUTS:
	cond:	string containing condition, eg: 'ge 5'.
	in1: vector to be checked for cond
 OPTIONAL INPUT PARAMETERS:
	in1: vector to be checked for cond
	in2,in3,in4: vectors with same no of elements as in1
	noapply_2: if set, condition will not be applied to 2nd input
	noapply_3,noapply_4: same for 3rd & 4th input
 OPTIONAL OUTPUT PARAMETERS:
	out1=in1(where(cl_vect eq class)),same for out2 & out3
		output vectors are 555 if list=-1
 EXAMPLE:
	list=select_cond('ne 0.0',i,in0,g,gn0)
 MODIFICATION HISTORY:
	31-Oct-2000  Original by Suzanne Aigrain
	17-nov-2000  S. Aigrain: added 4th vector and noapply keywords

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