Disallow commas in MySQL Manager's create/edit screens

I thought adding another IP in the hostname field like "localhost,8.8.8.8" would allow the user to connect via multiple sources. This didn't work, and screwed up MySQL and bugged the interface to the point where I had to delete the user via the root admin panel.

Don't allow comma's in these fields, and as an extra bonus, if they do include a comma, include a message along the lines "Users are only supported via one IP or hostname. If you need to add additional, add the same username/password with a different IP/hostname."