Only setup prototypes on constructors which are the direct target of new operations.

This is a simple change to removes the need to install a prototype on constructors which are merely used as targets of super()/this() calls.

http://gwt-code-reviews.appspot.com/176802/show
Review by: spoon


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7775 8db76d5a-ed1c-0410-87a9-c151d255dfc7