Make btcheck an alias for btinfo

[koobs]

I often forget eir commands and sometimes use !btcheck (or btcheck in privmsg) to get ban index information. btcheck doesn't result in any response from eir (as expected).

Add "btcheck" as an alias of the "btinfo" command

[agjmills]

As btcheck is a different command, this probably isn't feasible:
see the btcheck section on here: https://web.archive.org/web/20150919152436/https://freenode.net/eir.shtml