Rename js file to make minified file relationship clear

To close http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=736783, we should rename the "original" unminified source file ./doc/_themes/saltstack/static/js/vendor/modernizr.custom.20463.js to ./doc/_themes/saltstack/static/js/vendor/modernizr-2.6.2-respond-1.1.0.js

This should also be cherry picked to the 2014.1 branch