Support for beta 6

[Codeglee]

Only takes a couple of small changes to ConstraintAttributes for it to comply with BitwiseOperationsType.

RawOptionSetType, BooleanType

static var allZeros : ConstraintAttributes { return self(0) }

That's it.

[robertjpayne]

@Codeglee It's been added in the 'develop' branch. The develop branch requires a bridging header though as it's not pure Swift to allow for Objective-C backwards compatibility.

Once the GM seed is released hopefully next week we'll get this all tidied up!

[Codeglee]

Looking forward to it :)

[powerje]

Doh, I didn't even check for a develop branch before I made a PR for beta 6: #7