Fixed <rdar://problem/5065399> REGRESSION: leaks in Frame::bindingRootObject 
        seen on buildbot

        The problem was that we were initializing the same WebScriptObject twice.
        This caused it to leak its original set of ivars.
        
        I think some refactoring could prevent this situation from arising in the
        first place, but I'm just adding a check at the call site for now, to do 
        the simplest thing.

        * bindings/objc/WebScriptObject.mm:
        (-[WebScriptObject _setImp:originRootObject:rootObject:]): Added ASSERTs
        against multiple calls.

        * bindings/objc/WebScriptObjectPrivate.h: Renamed _initializeWithObjectImp
        to setImp because "init" vs "initialize" was a too subtle indication that
        one was a Cocoa initializer and one was not.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20240 268f45cc-cd09-0410-ab3c-d52691b4dbfc