Revisions: Use jQuery animation.

The CSS3 animations caused issues because the element was still there, and there is no standard way to know when a CSS3 animation is done.

See #24425.

git-svn-id: https://core.svn.wordpress.org/trunk@24660 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Revisions: Immediately do a disabled button check on `ready()`.

Solves the issue of Prev/Next buttons not being disabled on initial load, when routing to an extremity.

See #24425.

git-svn-id: https://core.svn.wordpress.org/trunk@24661 1a063a9b-81f0-0310-95a4-ce76da25c4cd