Etherpad Lite stupidly redirects to an absolute path, breaking reverse proxies

[MarkTraceur]

Thanks a lot for properly sanitizing URLs, but now when I have to do it behind a reverse proxy, EPL redirects to /p/padname. While that may be fine for the folks running on :9001 or so, I've got a reverse proxy running, so it should look like /pad/p/padname. Of course, EPL has no concept of this.

I'll probably fix this within 20 minutes, so stand by.

[MarkTraceur]

#833 fixes this.