SelfContained:  strip off fragment, query of relative URL

before treating as a filename.  This fixes `--self-contained`
when used with CSS files that include web fonts using the
method described here:

http://paulirish.com/2009/bulletproof-font-face-implementation-syntax/

Examples from reveal.js themes:

    "../../lib/font/league_gothic-webfont.eot?#iefix"
    "../../lib/font/league_gothic-webfont.svg#LeagueGothicRegular"

Closes #739.