Enable the use of the unpatched DirectX SDK to build Allegro.

See comment in the added code for explanation.
Rename the primitives buffer flags
Simplify the prim buffer hints
Simplify the al_create_vertex_buffer API
Fix build error
win: Fix compilation with D3D shader support disabled.

Also minor cleanup of the _al_d3d_on_lost_shaders,
_al_d3d_on_reset_shaders functions.
docs: Mark 5.0.10 additions.

al_destroy_bitmap convenience
ALLEGRO_SRC_COLOR
ALLEGRO_DEST_COLOR
ALLEGRO_INVERSE_SRC_COLOR
ALLEGRO_INVERSE_DEST_COLOR
Prepare summary of changes for 5.0.10.
Remove al_get/set_screen_scale as not really needed and confusing.
Remove generic audio event source and AudioQueue events.
Silence a warning.