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/weboobcli/weboobcli.py

@@ -42,7 +42,7 @@ class WeboobCli(ReplApplication):
     def main(self, argv):
         if len(argv) < 3:
             print >>sys.stderr, "Syntax: %s capability method [args ..]" % argv[0]
-            return 1
+            return 2
 
         cap_s = argv[1]
         cmd = argv[2]