Blender Git Loki

Bugfixes for Grease Pencil and the Image Editor (includes fix for #20921):

* Fixed crash with when/after undoing Grease Pencil sketches in the Image Editor. To get this working, I've had to sacrifice the backwards-compat loading for old .blend files from 2.49 which were using the same pointer as the new data (local data vs datablock data). If anyone has any ingenious hacks to fix this, go ahead, but otherwise, some caution is advised here...

* Grease Pencil block used for Image Editor instances can now be changed

* Enabled proper active polls on the advanced 3D-view projection methods for drawing. These are not valid in views other than the 3D-View, and so should not be shown as available for use elsewhere (though may still be shown just so that users know what mode an 'imported' datablock may be using).

* Enabled proper updates for Grease Pencil editing in the Image Editor. Was missing notifiers for this stuff.

* When drawing in the Image Editor with no image active, the system now (quietly) switches to using screen-space 'view' vs 'cursor' space for the strokes, since the previous behaviour was confusing with strokes disappearing after drawing them. IMO this is a much better option than the confusion that occurred before, even though it does change the user's settings under their feet!