Keep global scope clean with AMD. Always check for jQuery global.

If an AMD environment, don't export `UAParser` to global scope.
Even in AMD environment jQuery exports to global scope. We should catch it even then.
It also can happen then one joins the jQuery source file with other jQuery plugins in a CommonJS env.
Merge pull request #81 from duzun/patch-2

Keep global scope clean with AMD. Always check for jQuery global.