SUSORT - sort on any segy header keywords			

 susort <stdin >stdout [[+-]key1 [+-]key2 ...]			

 Susort supports any number of (secondary) keys with either	
 ascending (+, the default) or descending (-) directions for 	
 each.  The default sort key is cdp.				

 Note:	Only the following types of input/output are supported	
	Disk input --> any output				
	Pipe input --> Disk output				

 Note: If the the CWP_TMPDIR environment variable is set use	
	its value for the path; else use tmpfile()		

 Example:							
 To sort traces by cdp gather and within each gather		
 by offset with both sorts in ascending order:			

 	susort <INDATA >OUTDATA cdp offset			

 Caveat: In the case of Pipe input a temporary file is made	
	to hold the ENTIRE data set.  This temporary is		
	either an actual disk file (usually in /tmp) or in some	
	implementations, a memory buffer.  It is left to the	
	user to be SENSIBLE about how big a file to pipe into	
	susort relative to the user's computer.			


 Credits:
	SEP: Einar, Stew
	CWP: Shuki, Jack

 Caveats:
	Since the algorithm depends on sign reversal of the key value
	to obtain a descending sort, the most significant figure may
	be lost for unsigned data types.  The old SEP support for tape
	input was removed in version 1.16---version 1.15 is in the
	Portability directory for those who may want to input SU data
	stored on tape.

 Trace header fields modified: tracl, tracr