Let ejabberdctl accept binary string arguments

Don't print the following message if an ejabberd command expects binary
string arguments: "This command cannot be executed using ejabberdctl.
Try ejabberd_xmlrpc."
mod_register_web should response 404 instead of process crash.
Merge pull request #187 from weiss/fix-ejabberdctl-output

Let ejabberdctl accept binary string arguments
Merge pull request #190 from hamano/mod_register_web_response_404

mod_register_web should response 404 instead of process crash.