Better warning message.
Better warning message.

When using `model_name` option in the rule, controller doesn't find its
`target_object` and that is ok (reputation is still granted after).

Warning is still useful for newcomers who are not yet familiar with the
option.

[fixes #154]

raderj89/merit,iagopiimenta/merit,iagopiimenta/merit,caiqinghua/merit,caiqinghua/merit,iagopiimenta/merit,michael-gabenna/merit,woopasoft/merit,hw676018683/merit,michael-gabenna/merit,pablobfonseca/merit,hw676018683/merit,raderj89/merit,hw676018683/merit,caiqinghua/merit,woopasoft/merit,michael-gabenna/merit,pablobfonseca/merit,raderj89/merit,pablobfonseca/merit,woopasoft/merit