media rules implement nsIDOMCSSMediaRule. Fix insertRule() to be able
to insert into the middle of a rule list. Fix issues with stylesheets
not getting dirtied when media lists are modified. bug 93977,
r=pierre, sr=jst
tracking the attributes which appear in CSS selectors, and only firing
a complete reresolution when we change one of those. In the irrelevant-attr
case, we just let the frame update itself and get on with our lives right
away. Fixed 38378, r=brendan, booyah.
Also, when setting an attribute to the same value that it currently holds,
don't think about it especially hard, and _don't_ go anywhere near the
style code. Fixed 21879, r=brendan, boo_yah_.