REJOIN_PRB
   "Rejoin" a set of data files associated with
   a decomposition of a rectangular array of data
   into rectangular subarrays associated with
   NPX by NPY processors.
  
   The original region had a grid point shape of 
         100  by          100
  
   The processor array has the shape:
           4  by            2
  
   Therefore, the subarrays have shape:
          25  by           50
  
   The input parallel files are assumed to be formatted      
   The output serial file will be formatted      
  
   Requested conversion:
     Convert FIELD_T files.
  
 PFILE_OPEN_READ - Fatal error!
   Could not open one of the parallel files:
field_t_0000_0.000E+00.txt
  
 REJOIN_SAVE - Fatal error!
   Could not open the input parallel SAVE files.