Fixes #13571. jQuery.isPlainObject 1.9.x compatibility

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
Revert 8d1c42296fefc4e79189b6c2d78a8a78fdd9576d
No ticket: compare_size returns!
(remember to `npm install`)
Update Sizzle: minor windows 8 issue
Edited comments and minor adjustments. Fixes #13553. Closes gh-1195.