required validation in both IE10 in compatibility to IE8 and IE10 in compatibility to IE7

there is a Confirmed bug in IE10 compatibility view that won't be fixed for IE10:

In IE10 in compatibility to IE8 $element.get(0).getAttribute("required") returns "" when the required attribute is missing, this causes ALL fields to be required

In IE10 in compatibility to IE7 
$element.get(0).getAttribute("required") returns null in all cases.
but .attributes["required"].value returns "-1" if it exists and "null" otherwise
so handling these edge cases for developers that want to check compatibility view (the plugin Author doesn't plan to handle compatibility views)