Made the function definition related to UA environment, matchMedia check only happened once.
add new feature-detect for DOM 3 Document Fragments
reports true as expected in IE 6-10, Chrome, Opera
Merge pull request #641 from jokeyrhyme/master

feature-detect for Document Fragments
Merge pull request #1034 from swaydeng/pr_mq

Code refactoring, made the function definition related to UA env