[AD] Making the projection transform bitmap local

[SiegeLord <slabode@xxxxxxxxxx>]

The projection transform being display-local has been a wart in Allegro 
for quite a long time. Unlike every other global state, the projection 
transform was extremely volatile... if you looked at Allegro wrong, it 
would reset it to orthographic... the only practical way of using it is 
to reset it to the desired transformation pretty much all the time 
before drawing. There is in fact a bug about this 
http://sourceforge.net/p/alleg/bugs/349/ submitted by myself 3 years ago 
which involved the font addon not properly restoring it after it was 
clobbered by an intra-addon al_set_target_bitmap call.

After a year of on and off work (it wasn't a priority), I managed to 
change it to be a bitmap local state. Now, it is acts essentially the 
same as the regular bitmap transform, and it preserves its set value at 
in all situations except two:

- The backbuffer bitmap's projection transform reverts back to 
orthographic when it is resized (simultaneously with the 
al_acknowledge_resize call).
- A video bitmap's projection transform reverts back to orthographic 
when it is converted to a memory bitmap (those only support orthographic 
transforms).

I think it works pretty good, actually and resulted in some 
simplification in the internals' code. Some other benefits of this 
change include these projection transforms actually working properly for 
sub-bitmaps (they did not work reliably before this change).

This mostly affects people who use projection transforms (naturally), 
but it also affects people who don't in the following way:

- iOS now sends the resize events somewhat more often (this shouldn't be 
a big issue)
- Android now sends a resize event after 
ALLEGRO_EVENT_DISPLAY_RESUME_DRAWING. This is to allow 
ALLEGRO_EVENT_DISPLAY_RESUME_DRAWING event to not change the 
backbuffer's transform (instead, the user simply needs to handle the 
resize event and everything will happen automagically).

Obviously, as this touched some hairy code, this might introduce some 
bugs, but I've tested this somewhat extensively on all our core 
platforms (except a physical iOS device... I don't have one, so I could 
only use the simulator).

Check out the implementation here: 
https://github.com/liballeg/allegro5/pull/13

And in patch form: https://github.com/liballeg/allegro5/pull/13.patch

Some migration notes:

al_get_projection_transform(display)

changes approximately to (might need to insert a al_set_target_bitmap() 
call):

al_get_current_projection_transform()


al_set_projection_transform(display, &trans)

changes approximately to (might need to insert a al_set_target_bitmap() 
call):

al_use_projection_transform(&trans)

That said, in principle you should be able to remove many 
al_set_projection_transform calls altogether if all you were doing is 
resetting them every frame. Now you can just set it and forget it 
(except for the two cases outlined above).

Some implementation notes:

The display retains a cached 'projview' transform for the purposes of 
shaders, but otherwise everything is set up in the update_transformation 
method in the ALLEGRO_DISPLAY_INTERFACE.

-SL