Reviewed by Oliver Hunt.
        
        Removed and/or reordered exception checks in array-style a[n] access.
        
        SunSpider says 1.4% faster.

        * VM/Machine.cpp:
        (KJS::Machine::privateExecute): No need to check for exceptions before
        calling toString, toNumber and/or get. If the call ends up being observable
        through toString, valueOf, or a getter, we short-circuit it there, instead.
        In the op_del_by_val case, I removed the incorrect comment without actually
        removing the code, since I didn't want to tempt the GCC fates!

        * kjs/JSObject.cpp:
        (KJS::callDefaultValueFunction): Added exception check to prevent
        toString and valueOf functions from observing execution after an exception
        has been thrown. This removes some of the burden of exception checking
        from the machine.

        (KJS::JSObject::defaultValue): Removed redundant exception check here.

        * kjs/PropertySlot.cpp:
        (KJS::PropertySlot::functionGetter): Added exception check to prevent
        getter functions from observing execution after an exception has been
        thrown. This removes some of the burden of exception checking from the
        machine.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@34945 268f45cc-cd09-0410-ab3c-d52691b4dbfc