BBCodeText: Escape BBCode

[robinheidrich]

It would be really nice to be able to exclude user-made messages from BBCode.

For example:

A message with [b]BBCode[/b] and an [esc][b]escaped message[/b][/esc].

would output:

A message with BBCode and an [b]escaped message[/b].

Just an example, maybe it can be done differently.