Redo V3Life to also do constant propagation

git-svn-id: file://localhost/svn/verilator/trunk/verilator@796 77ca24e4-aefa-0310-84f0-b9a241c72d87

src/Verilator.cpp

@@ -327,6 +327,7 @@ void process () {
     v3Global.rootp()->dumpTreeFile(v3Global.debugFilename("clock.tree"));
 
     // Cleanup any dly vars or other temps that are simple assignments
+    // Life must be done before Subst, as it assumes each CFunc under _eval is called only once.
     if (v3Global.opt.oLife()) {
 	V3Life::lifeAll(v3Global.rootp());
     }