mshtml: Added IHTMLLocation::assign method implementation.

[Nikolay Sivov]

>       HTMLLocation *This = impl_from_IHTMLLocation(iface);
> -    FIXME("(%p)->(%s)\n", This, debugstr_w(bstr));
> -    return E_NOTIMPL;
> +    TRACE("(%p)->(%s)\n", This, debugstr_w(bstr));
> +    return HTMLLocation_put_href(iface, bstr);
I don't know if it correct or not, but please use method wrappers when 
calling from interface pointer instead of calling implementation directly.