[AD] locking problem on OpenGL

[Peter Wang <novalazy@xxxxxxxxxx>]

In ex_bitmap.c if I comment out al_set_new_bitmap_flags(ALLEGRO_MEMORY_BITMAP);
and load a JPEG image then the output comes out wrong.  It looks like it
is expecting 4-channel data and only getting 3-channels.  I'm pretty
sure the JPEG loader is correct.  It works with memory bitmaps and D3D
under Wine.  I tracked this down as far as the glTexSubImage2D() calls
in ogl_unlock_region.  The bug only occurs with ALLEGRO_LOCK_WRITEONLY.

Also, not really related, but in ex_pixelformat I saw that these
conversions had problems:
	RGBA8888 -> RGBA4444
        BGR888   -> RGBA4444       
	BGR555   -> RGBA4444       
	RGBX8888 -> RGBA4444       

Peter