While working on the next significant hunk of changes towards 47679, I 
saw a few more obvious cleanups that ought to happen.

First, we have a policy for data members that they ought to be prefixed 
with m_ to denote the extra overhead in accessing those members.  The 
data member in the const_and_copies unwinder stack didn't have the 
prefix.  This patch fixes that oversight and the obvious fallout.

It also adds an additional high level comment for the const_and_copies 
stack and updates an out-of-date comment in tree-ssa-dom.c.

This was extracted out of a larger patch that has bootstrapped and 
regression tested on x86_64.  This patch was quick-strapped to ensure it 
didn't break anything.

This is (of course) related to BZ47679.


Installed on the trunk.

Jeff