Fix identifier lookups when mixing variables and arguments

Fix identifier lookups when mixing variables and arguments

Suppose the following test-case:

function outter() {
    var foo = "bar";
    function inner(foo) {
        function innerMost() {
            print(foo);
        }
        return innerMost();
    }
    inner("FOO");
}

When looking up "foo" in innerMost we used to find the variable foo in outter,
because our fast lookup optimization doesn't take function parameters in outter
scopes into account. However we are supposed to find the parameter "foo" from
inner's activation object.

This fixes the last issue with running the Boyer benchmark.

Change-Id: I645ed1c601aff835bc9b7ee1fcfbdfa9c295a70c
Reviewed-by: Lars Knoll <lars.knoll@digia.com>