Patch to set zip filename to docid
Johnoel sent a some modification to code for action=export. The file which is
sent back to the user doesnt have .zip in the end and has a very generic name.
So Johnoel requested addition of this line of code in MetaCatServlet.java which
sets the name of the file to <docid>.zip
response.setHeader("Content-Disposition", "attachment; filename=" + docId