Begin implementing SimpleMesh and fix some bugs with refcounting and java object destruction tracking.
diff --git a/graphics/java/android/renderscript/ProgramFragment.java b/graphics/java/android/renderscript/ProgramFragment.java
index c228cf2..09c4d9a 100644
--- a/graphics/java/android/renderscript/ProgramFragment.java
+++ b/graphics/java/android/renderscript/ProgramFragment.java
@@ -46,8 +46,11 @@
     }
 
     public void destroy() {
+        if(mDestroyed) {
+            throw new IllegalStateException("Object already destroyed.");
+        }
+        mDestroyed = true;
         mRS.nProgramFragmentStoreDestroy(mID);
-        mID = 0;
     }
 
     public void bindTexture(Allocation va, int slot)