Allow a server hostname override for JIDs

[eshear]

Right now if you want to connect with Jabber::Simple using a gmail address which doesn't end in @gmail.com (for example, if you're using google apps for domains), it will break, because it will attempt to look up the talk server for your apps-for-domains location. I added an override so you can provide a server to connect directly to.

I think I sent this request already but I wanted to try the new pull-request system.

[thelinuxlich]

+1 for this

[frost-nzcr4]

Added in #13