Made output image name optional, so that matrix can be written to stdout like with fslswapdim

fslreorient2std

 #!/bin/sh
 
-if [ $# -lt 2 ] ; then 
-  echo "Usage: `basename $0` <input_image> <output_image>"
+if [ $# -lt 1 ] ; then 
+  echo "Usage: `basename $0` <input_image> [output_image]"
   echo " "
   echo "`basename $0` is a tool for reorienting the image to match the"
   echo "approximate orientation of the standard template images (MNI152)."
@@ -10,6 +10,8 @@ if [ $# -lt 2 ] ; then
   echo "It requires NIfTI images with valid orientation information"
   echo "in them (seen by valid labels in FSLView).  This tool"
   echo "assumes the labels are correct - if not, fix that before using this."
+  echo "If the output name is not specified the equivalent transformation"
+  echo " matrix is written to the standard output"
   echo " "
   exit 1
 fi