Use BooleanType instead of LogicValue

This is an update for Beta 5.  `LogicValue` has been renamed `BooleanType` and the protocol changed to be a `boolValue` property rather than the `getLogicValue` method.

Also updated the tests per the Beta 5 [release notes](https://developer.apple.com/devcenter/download.action?path=/Developer_Tools/xcode_6_beta_5_za4gu6/xcode_6_beta_5_release_notes.pdf):

> Optionals no longer conform to the BooleanType (formerly LogicValue) protocol, so they 
may no longer be used in place of boolean expressions (they must be explicitly compared with 
v != nil). This resolves confusion around Bool? and related types, makes code more 
explicit about what test is expected, and is more consistent with the rest of the language.