CREATE POSTSCRIPT FILE 
Macro: I_OPOSNOR
Function: Copies an image plane to a PostScript file which can be sent to a laser printer (with the instruction "lpr -P...file_name).
Parameters:
1. Image plane from which image saved as postscript file.  
2. Filename and directory.
Directory name should not end with '/'. If file does not exist requests another name.
