Improve the error message, when the parameter is not found.

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@53905 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/python/pygrass/modules/__init__.py

@@ -471,7 +471,7 @@ class Module(object):
                 # verbose and quiet) work like parameters
                 self.flags_dict[key].value = val
             else:
-                raise ParameterError('Parameter not found')
+                raise ParameterError('%s is not a valid parameter.' % key)
 
         #
         # check reqire parameters