Blender Git Loki

bugfix
* sliders with realtime option enabled did not have the correct event offset. (probably my fault when adding UIBlock/callbacks)
* callbacks could crash if they were free'd before the script ran them,
solved this by using weakrefs to the python function rather then the function its self in the buttons callback value.
Also store a list these weakref's in the Draw module's C file that are removed when the callback function is deallocated by python
(using pythons own weakref callback) - if the weakref is not in the weakref callback list then we know it has been deallocated and can report an error that it needs to be made global.

Tested this to work in UIBlock and normal button drawing.

Some other small cleanup also.