Turn on V8 by default.

This change requires clean libwebcore, but I saw there are three clean libwebcore_intermediates steps in build/cleanspec.mk already. Do I need to add another one?
diff --git a/Android.mk b/Android.mk
index 33c5bf0..38d1e04 100644
--- a/Android.mk
+++ b/Android.mk
@@ -35,9 +35,9 @@
   else
     # No JS engine is specified, pickup the one we want as default.
     ifeq ($(USE_ALT_JS_ENGINE),true)
-      include $(LOCAL_PATH)/Android.v8.mk
-    else
       include $(LOCAL_PATH)/Android.jsc.mk
+    else
+      include $(LOCAL_PATH)/Android.v8.mk
     endif  # USE_ALT_JS_ENGINE == true
   endif  # JS_ENGINE == v8
 endif # JS_ENGINE == jsc