[C] Change unknown command message to match vanilla. Fixes BUKKIT-4614

## The Issue

The unknown command message does not match the vanilla unknown command message.

## Justification for this PR

This should match vanilla behaviour. It also remedies the issue of players being instructed to type "help" (when doing so does nothing).

## PR Breakdown

The message was modified to match the default vanilla message. When a player is the sender, the coloring is ```ChatColor.RED```. When the console is the sender, the message is prefixed with ```ChatColor.RESET```.

## Testing Results and Materials

![screenshot on 2013-07-30 at 16 10 08](https://f.cloud.github.com/assets/406387/882142/afce1d34-f95c-11e2-8384-cbac16ca8dc5.png)

## JIRA Ticket

BUKKIT-4614 - https://bukkit.atlassian.net/browse/BUKKIT-4614