Implement the first half of redundancy factoring: efficiently  splitting all the patterns under scope nodes into equality sets based on their first node.  The second step is to rewrite the graph info a form that exposes the sharing.  Before I do this,  I want to redesign the Scope node.
Implement the first half of redundancy factoring: efficiently 
splitting all the patterns under scope nodes into equality sets
based on their first node.  The second step is to rewrite the
graph info a form that exposes the sharing.  Before I do this, 
I want to redesign the Scope node.



git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@97130 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx