Reviewed by Oliver Hunt.
        
        Sped up property access for array.length and string.length by adding a
        mechanism for returning a temporary value directly instead of returning
        a pointer to a function that retrieves the value.
        
        Also removed some unused cruft from PropertySlot.
        
        SunSpider says 0.5% - 1.2% faster.

        NOTE: This optimization is not a good idea in general, because it's
        actually a pessimization in the case of resolve for assignment,
        and it may get in the way of other optimizations in the future.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@35806 268f45cc-cd09-0410-ab3c-d52691b4dbfc