buttonMarkup: Use new $.mobile.getAttribute syntax to avoid concatenating with a prefix.

http://jsperf.com/buttonmarkup-centralize-prefix-adding
Widget: Use new $.mobile.getAttribute syntax to avoid concatenating with a prefix.
Popup: Hide popup when offscreen. Fixes #5892.
Custom select: Must un-hide popup container before calculating height.
Custom select: Escape weird characters in popup/dialog ID when they become hrefs. Fixes #5893.
package.json: Need to upgrade to later grunt-contrib-jshint to stop the linter from making false accusations.
Lint: Heeding the new version.