RegFieldDesc: Prevent different RegField JSONS from overwriting eachother.

src/main/scala/util/GeneratorUtils.scala

@@ -139,7 +139,12 @@ trait GeneratorApp extends App with HasGeneratorUtilities {
 
 object ElaborationArtefacts {
   var files: Seq[(String, () => String)] = Nil
-  def add(extension: String, contents: => String) {
+
+  def add(extension: String, contents: => String) = {
     files = (extension, () => contents) +: files
   }
+
+  def contains(extension: String): Boolean = {
+    files.foldLeft(false)((t, s) => {s._1 == extension | t})
+  }
 }