[tree-ssa] Insert on edge comment

[law@redhat.com]

In message <Pine.LNX.4.44.0305311132300.22731-100000@nondot.org>, Chris Lattner
 writes:
 >IMO, the real problem in tree-ssa is that it uses a nested control flow
 >structure instead of a linearized one...
Amen.  It's a model I'd like to move away from, it introduces a fair
amount of complexity.  However, it's pretty far down on the list of
things to do right now, but it's definitely on my list.

Jeff