Make Tor Browser follow the Tor Friendly Applications Best Practices doc

If I want to run two TBB 3.5's at once, I'm out of luck because the Tor ports conflict and they're hard-coded.

Vidalia solved this by having a checkbox for 'choose ports automatically', which starts Tor with "socksport auto" and "controlport auto" and then reads the file specified to Tor by ControlPortWriteToFile to learn what control port it picked.

Should we teach Tor Launcher to do something similar?

Maybe a reasonable place for the interface toggle is in the proxy settings window?