Fixed <rdar://problem/3964634> undefined property value from binding seems to evalua...

	Fixed <rdar://problem/3964634> undefined property value from binding seems to evaluate to true in an if statement

	The comprehensive fix for this problem requires new API, as described in 3965326.  However,
	given that we can't add new API at this point, the 'ObjcFallbackObjectImp' will behave
	like and Undefined object if  invokeUndefinedMethodFromWebScript:withArguments: isn't
	implemented on the bound object.

        Reviewed by Chris.

        * bindings/objc/objc_runtime.h:
        * bindings/objc/objc_runtime.mm:
        (ObjcFallbackObjectImp::type):
        (ObjcFallbackObjectImp::implementsCall):
        (ObjcFallbackObjectImp::toBoolean):
        * bindings/testbindings.mm:
        (+[MyFirstInterface isSelectorExcludedFromWebScript:]):
        (+[MyFirstInterface isKeyExcludedFromWebScript:]):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@8418 268f45cc-cd09-0410-ab3c-d52691b4dbfc