Selector: Remove "#" exception for identifier tokens

Port Sizzle test change from:
https://github.com/jquery/sizzle/commit/f204a6112216f31685717d9fc1bf6cabf42b2ef1
Build: update Sizzle to 2.0.0
Core: Consistently use local reference to access()

Ref 3b53b75160606610cc8f87404f89fc9e10441c4b
Closes gh-1605
Readme: Fix punctuation in tile

Closes gh-1607
Ajax: Remove workaround for IE6/7

Closes gh-1597
Ref #8138