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/geolooc/geolooc.py

@@ -37,9 +37,7 @@ class Geolooc(ReplApplication):
     def main(self, argv):
         if len(argv) < 2:
             print >>sys.stderr, 'Syntax: %s ipaddr' % argv[0]
-            return 1
+            return 2
 
         for backend, location in self.do('get_location', argv[1]):
             self.format(location)
-
-        return 0