switch branches must be declared required so that the compressor doesn't

replace nodes with a single statement.

looks stable for now, though mess begins to sink in.  need to review the AST
hierarchy.

lib/ast.js

@@ -304,11 +304,17 @@ var AST_Switch = DEFNODE("Switch", "expression", {
 }, AST_Statement);
 
 var AST_SwitchBlock = DEFNODE("SwitchBlock", null, {
-    $documentation: "The switch block is somewhat special, hence a special node for it"
+    $documentation: "The switch block is somewhat special, hence a special node for it",
+    initialize: function() {
+        this.required = true;
+    },
 }, AST_BlockStatement);
 
 var AST_SwitchBranch = DEFNODE("SwitchBranch", null, {
-    $documentation: "Base class for `switch` branches"
+    $documentation: "Base class for `switch` branches",
+    initialize: function() {
+        this.required = true;
+    },
 }, AST_BlockStatement);
 
 var AST_Default = DEFNODE("Default", null, {