Warn if user runs /quote /command

[DanielOaks]

We had an issue where someone was trying to run SAMODE, but needed to use /QUOTE to do it. They were running /QUOTE /SAMODE and Ora was returning that there wasn't a command called that, which was pretty confusing to work out.

If an unknown command starts with /, we should probably return a more specific message with the unknown command numeric, e.g. maybe Unknown command. The command you tried to run was accidentally prefixed with a /, try running it without the leading slash or something along similar lines.