Fix #messageRoom

Depending on whether messageRoom or reply is used, the channel could be either a C****** slack channel code or the literal name, like 'general'. The former can be passed directly; the latter requires leading with a pound sign. So, this fixes #messageRoom without breaking #reply.

I'd love to update the tests, but I have no idea how to run them. So, if anyone wouldn't mind posting a link or some instructions, that would be great.