fix browser detection for jQuery > 2.0

jQuery removed $.support.leadingWhitespace from jquery greater 2.0
because support was dropped for IE 7/8. So if property is undefined,
we are pretty shure its ie > 8 or jQuery does not support the browser
anyway.
no confusing use of "!"
add comment to browser detection
Merge pull request #1246 from bastjan/0.9-work

Fix browser detection for jQuery > 2.0