Fixed that some Mojang users without Minecraft Premium got Illegal Name error.
This happens because Mojang users log in with their e-mail address and not with their username.
When the user has bought Minecraft, the message received to the server is their username.
But if they haven't, their e-mail address is used.
When the email address contains the character '-' it's not allowed by the server.
Now the allowed characters contains '-' only whenever a mojanguser without Premium logs on to the server.