Get rid of StSw craziness and use lsllastpass to make another pass.

This has been a TODO item for long. Now that we have lsllastpass, it's actually easy to implement.

Adds an LSLTypeDefaults dictionary to lslcommon, just in case the state-changing function returns a value and we need to insert a return statement.

We've also added subtree-local info to lsllastpass (lost when we return to the parent after visiting a subtree).

This fixes a bug where naked switch statements could appear as a result of optimization, and cause the compilation to fail.

testparser.py

@@ -272,7 +272,7 @@ class Test03_Optimizer(UnitTestCase):
             vector vvvv2=vvvv;
             float ffff3 = v.z;
             integer fn(){
-                if (1) state default; else return 2;
+                if (1) state default;
                 return fn();}
 
             default{touch(integer n){