Re-introduce SC.Error#throw where throw has been renamed $throw to prevent a crash with YUI

Same goal as https://github.com/sproutcore/sproutcore/pull/1279 with a renamed throw method for YUI (as reported here https://github.com/sproutcore/sproutcore/issues/1297).

To summary, this change allow SC.Error to correctly throw error by instantiating an `Error` object first. This is needed to get a correct stacktrace. Currently errors throw in SC do not get a correct stacktrace.