CREATE POSTSCRIPT FILE 
Macro: I_OPOSMAX
Function: Save image as PostScript file to send to a laser printer (with the instruction 'lpr -P...file_name'). The printed image is enlarged.
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.
