	PRCSTK applies the PROCESS procedure to each spectrum indicated
	by the scan numbers stored in the ASTACK array.  Scans 
	located at the same position on the sky (within the specified
	tolerances and using the XSOURCE and YSOURCE header values)
	are ACCUMed (with no SHIFTing applied).  The processed and
	ACCUMed scans are saved to the a save file.  Users have the option
	of saving the current save file (either by writing over any
	contents of the file or by appending to the file), creating a
	new, empty save file (the current save file would need to be
	re-attached using CHNGFILE after this procedure runs if you wish
	to return to using it as the save file), or exiting from the
	procedure if none of those options is acceptable.  The global 
	adverb MAXNSAVE is set to the highest value of NSAVE used.  
	The save file must either be empty or you must have set 
	SPROTECT=FALSE to allow the data to be written over.  An
	append will only work if MAXNSAVE is set to the last scan in
	use before using PRCSTK.

	Syntax: PRCSTK(x_tol, y_tol)

	x_tol and y_tol are pointing tolerances -- any two scans located
	within these distances from each other are considered to be taken
	at the same location and will be averaged using ACCUM.  x_tol 
	and y_tol are in arcseconds and cannot be zero.

	This procedure is useful in preparing a SAVE file that is
	appropriate for use by the other mapping procedures included in
	maps.plib.

	The data is fetched using GET and the values in the ASTACK array.

	This procedure uses the SORTSTK procedure to sort the coordinates.
	You should read the documentation for SORTSTK for more information
	on what that procedure does.  The temporary file used by
	SORTSTK is prcstk.temp.  This file is deleted upon successful
	completion of PRCSTK.  It must not exist at the start of
	PRCSTK.

	This procedure uses PROCESS to process each scan.  You should 
	read the documentation on what that procedure does.  If you wish
	to alter how each scan is processed, you should edit a copy of 
	PROCESS.  If you wish to add a SHIFT step to this process, you
	should edit a copy of PRCSTK.  You should test out PROCESS on
	a representative scan before processing the entire ASTACK array
	to be certain that PROCESS does what you expect it to do.

	File name: prcstk.prc

	This procedure is included in maps.plib

	Dave Burrows made significant contributions to this procedure.

	Example:

	You want to make a map having pixels 30x20 arcseconds in area.
	You have already loaded the scan numbers of the data that will
	make up this map in to the ASTACK array (e.g. by using SELECT).
	You want to process each scan and average any scans at the
	same mapping pixel and produce a new SAVE file to be used
	by CUBEINPUT (to make a cube using cube.exe).  So you type:

		> CHNGFILE CREATE SSCANS NewSave.SDD
		># The next two steps verify that PROCESS does what
	        ># I want it to do, any adverbs that PROCESS may
		># use should be set prior to its use.
		> GET ASTACK(1)
		> PROCESS; PAGE; SHOW
		> PRCSTK(30, 20)
		> MAXNSAVE = 0
		Current SAVE file contains 0 scans.
		Select an option:
			0: append new data to end of existing SAVE file
			1: overwrite existing SAVE file with new data
			2: create new SAVE file
			3: exit routine
		# 0

	And the results of the procedure will be written to your
	screen.  New positions are separated by "-------------".
	On each line between the above string is printed the
	scan number, x, and y positions.

	NOTE: MAXNSAVE is reset to 0 since this is a new file.  
	      Alternatively, you could have omitted the CHNGFILE step
	      as well as the MAXNSAVE setup above and simply chose
	      option 1.  You would have then been asked what the
	      name of the new SAVE file should be.  The result would
	      have been identical.

	NOTE: The zero after the hash symbol, #, by itself above is
	      the response that the user typed.

	The results are saved to the save file you just created.
	You could then run CUBEINPUT by typing:

		> CUBEINPUT(30,20)
