ban regexp compilation is broken

[slingamn]

https://github.com/oragono/oragono/blob/d37af694af3c9440c3b44725325f97f3c5ddbd1d/irc/client_lookup_set.go#L455

Because there are no parentheses surrounding the inner expression, the ^ and the $ get "stuck" to the initial and final sub-expressions.

[slingamn]

Specifically, the buggy behavior is with the final | expression, which gets stuck to the $ but not the ^, so it matches any prefix on top of that final expression.

This bug goes back to d4093e7, which is rather moving. @jlatt, we miss you <3