Better messages and return codes in applications

Use stderr and return codes >0 when it makes sense.
Loose return code conventions:
* 1 for generic errors
* 2 for user input errors
* 3 for remote errors (not found, etc.)
* 4 for not implemented

weboob/applications/weboorrents/weboorrents.py

@@ -113,6 +113,7 @@ class Weboorrents(ReplApplication):
 
         if not found:
             print >>sys.stderr, 'Torrent "%s" not found' % id
+            return 3
         else:
             self.flush()
 
@@ -149,6 +150,7 @@ class Weboorrents(ReplApplication):
                 return
 
         print >>sys.stderr, 'Torrent "%s" not found' % id
+        return 3
 
     def do_search(self, pattern):
         """