jquery event: closes #4033. e.currentTarget wasn't being enforced for native events (IE doesn't have it)

fix show issue in IE 6. "olddisplay" is sometimes undefined and IE 6 does not like setting style.display to undefined. also second for loop was mistakenly nested within the first for loop.

Added support for class selectors and class attribute selectors on XML documents. Fixes jQuery bug #4167.

Change the behavior of how :visible and :hidden work. :hidden is when an element is display none, a parent element is display none, or the element has a width of 0. :visible is when the element is not display none and all of its ancesotrs are not display none and its width is larger than 0. Fixes jQuery bugs #1349, #3265, and #3895.

Fixed a bug with certain + selectors failing (Fixes jQuery bug #4023). Also tweaked the + and > functions a little bit.

Make sure that [name=FOO] searches actually have the specified name (IE includes elements that have the ID, as well).

Added fixes for two different :not() bugs. One with p:not(p.foo) failing and another with a weird combination of multiple selectors and filters. Fixes jQuery bug #4101.

Provide a graceful failover for [name=foo] queries that are looking for non-input/iframe/form elements. Fixes jQuery bug #4081.

The compareDocumentPosition check was extraneous - indexOf works in all the other browsers that we need to support.

Added some significant speed-ups to height/width checks, thanks to some code and investigation by Mike Helgeson. Fixes #3082.

Landing a fix for a case where the animation timer wasn't getting stopped (thanks Arrix). Fixes bug #4001.

Fixed bubbling of live events (if an inner element handles an event first - and stops progatation - then the parent event doesn't encounter the event). Thanks to Irae for the patch. Fixes bug #3980.

Added a performance improvement to .hide()/.show() that helps to prevent constant reflows from occurring. Fixes #4038.

Optimized the clean() code to no longer use .trim() (speeds up working against long HTML in IE). Fixes #4037.

Reworked the attribute selection code to be able to select false-y values - and added some tests to verify that they work well against expandos.

Reworked the .clone() function in IE. Fixes jQuery bugs #3500 (jQuery expandos were causing extra elements to appear from using .html() cloning), #3254 (Mis-match in clone result length causes problem), and #2845 (Cloning an <object/> causes exceptions to be thrown).

Added logic for not using getElementsByClassName in different failure states. Fixes jQuery bugs #4058 and #4042.

Made the getAttribute check more explicit - comment nodes don't have getAttribute in XUL documents. Fixes jQuery bug #3870.