objects:

  FT_Face_Internal, FT_Size_Internal, FT_Slot_Internal

these contain some fields that may change between releases
of FreeType, without affecting the size of FT_FaceRec,
FT_SizeRec, FT_GlyphSlotRec, etc.., which means that
drivers wouldn't need to be recompiled if we only add new
fields to an internal structure..

I plan to hack a few things related to the auto-hinter and
I need this move to ensure that we will not break binary
compatibility between 2.0 and 2.1 :-)

- David