Use parser error rather than systemexit exception

src/filter.py

@@ -142,12 +142,12 @@ class Filter(object):
         self._client_dest = Client(args.dest_url)
 
         if (not self.interhost) and (args.srcpath == args.destpath):
-            raise Exception("source and destination path must be different")
+            self._parser.error("source and destination path must be different")
 
         # Open and print info about the streams
         self.src = get_stream_info(self._client_src, args.srcpath)
         if not self.src:
-            raise Exception("source path " + args.srcpath + " not found")
+            self._parser.error("source path " + args.srcpath + " not found")
 
         self.dest = get_stream_info(self._client_dest, args.destpath)
         if not self.dest: