remove a dependency of GraphicBuffer (libui) on Parcel (libbinder).

Add a Flattenable interface to libutils which can be used to flatten
an object into bytestream + filedescriptor stream.
Parcel is modified to handle Flattenable. And GraphicBuffer implements
Flattenable.

Except for the overlay classes libui is now independent of libbinder.
diff --git a/libs/utils/Android.mk b/libs/utils/Android.mk
index d2cfd3b..d0eedb4 100644
--- a/libs/utils/Android.mk
+++ b/libs/utils/Android.mk
@@ -25,6 +25,7 @@
 	CallStack.cpp \
 	Debug.cpp \
 	FileMap.cpp \
+	Flattenable.cpp \
 	RefBase.cpp \
 	ResourceTypes.cpp \
 	SharedBuffer.cpp \