Fix clear() operation for rsScriptC.

- This removes a memory leak where some elements were not getting tracked
  properly (and then triggering an assert when a context is destroyed).
- Convert ScriptCState to use a tracked object reference for mScript.
- Add a missing clear to FontState.
- Clean up synchronization in RSTest so that our graphics context outlives
  any subtest context.

Change-Id: I0d5768c4d2f8810dd1ae2f68b1edd7e150f382fd
diff --git a/rsContext.cpp b/rsContext.cpp
index b4d5014..cfd6479 100644
--- a/rsContext.cpp
+++ b/rsContext.cpp
@@ -294,6 +294,7 @@
          LOGE("pthread_setspecific %i", status);
      }
 
+     rsc->mScriptC.init(rsc);
      if (rsc->mIsGraphicsContext) {
          rsc->mStateRaster.init(rsc);
          rsc->setRaster(NULL);