Strange behavior of attr method when generate input element.

[Soul_Master]

I try to set attr of input element by using boolean type. But the result is very strange for me.

​http://jsfiddle.net/hsh8m/

[Timmy Willison]

Construct boolHook and rboolean regex to deal with boolean attributes. Fixes #9129. Fixes #9123.

• Construct regex for all attributes which are boolean attributes by specification.

+ This allows us to do what users expect with enumerated attributes and allows us to no longer complicate the issue.

+ People are just too confused with passing "true" instead of true when they should, so we won't have to worry about that anymore.

• Modularize code for dealing with boolean attributes into a separate hook to keep attr short and fast. Changeset: 5097e6d1c672ef5fd3fcc0022ce84519233189cc