rtgui_blit: adjust the info

When the source and destination is not match, we need to adjust the info
before going into the underlaying drivers.
Merge pull request #72 from grissiom/fix-blit

rtgui_blit: adjust the info
anim: no need to check fc_buf or max_tick on _start
anim: engine_move: do not draw absent buffers
anim: move engines to animation_engines.c
dc_buffer: check malloced dc->pixel in creation

If the malloced dc->pixel is NULL, return NULL.
animation: add fade engine
blit: Blit565to565PixelAlpha: cope with alpha 255

Alpha is uint8 thus 0~255. Dividing it with 8 result in 0~31. So we
could not get the full src channel even if when alpha is 255. Add a
special case to handle that.
blit: optimize Blit565to565PixelAlpha
app: check against deleted objects when sending events

There is a chance that when the event arrived, the destnation objects
has already been deleted. This commit add magic bits in the object flags
and check it before dispatching the events to window.