Added browser.versionNumber and linted jquery.browser.js.

I use this library mainly to check browser versions, and have found that some version numbers don't convert well for comparison. For example, Chrome is currently version 31.0.1650.48, which becomes NaN. I've added browser.versionNumber which uses parseFloat to correctly change this to a number (it will return 31). I recommend using this for any version number checks, rather than the version string.

I also linted the JS file, removing some trailing whitespaces and such.