Fixed bug 613153:  https://bugs.launchpad.net/leo-editor/+bug/613153 unable to describe root directory on thumb drive

The solution is to use the %~dp0 syntax:
http://ss64.com/nt/syntax-args.html
http://stackoverflow.com/questions/5034076/what-does-dp0-mean-and-how-does-it-work

Added a FAQ Entry: LeoDocs.leo#Leo's Documentation-->FAQ-->@rst html\FAQ.html-->Tips and techniques-->How can I specify the root directory of a thumb drive?

Leo build: 20141030050004