Enhance unittest_graphic_gcontext

The text thread now checks that it
freed all resources before exit.

(Test have to run twice cause the first
time EGL allocates aditional resources.)
Rename XXX_INIT_FREEABLE into XXX_FREE

The static object initializer XXX_FREE
initiailizes objects of type XXX into a freed state.
Calling free_XXX on an already freed object
does no harm.
Implement ptr module

The module abstracts setting, clearing and reading
the least significant bits of an aligned pointer.