engine, lib: Misc log and comment changes

Just misc polishing.

engine/graph/engine.go

@@ -144,7 +144,7 @@ func (obj *Engine) Validate() error {
 		}
 
 		if err := engine.Validate(res); err != nil {
-			return errwrap.Wrapf(err, "the Res did not Validate")
+			return fmt.Errorf("%s did not Validate: %v", res, err)
 		}
 	}
 	return nil

engine/graph/reverse.go

@@ -275,7 +275,7 @@ func (obj *State) ReversalWrite(str string, overwrite bool) error {
 		if str != oldStr {
 			obj.Logf("existing, pending, reversible resource exists")
 			//obj.Logf("diff:")
-			//obj.Logf("") // TODO: print the diff w/o and secret values
+			//obj.Logf("") // TODO: print the diff w/o secret values
 			return fmt.Errorf("existing, pending, reversible resource exists")
 		}
 	}