Blender Git Loki

Grease Pencil: Restored some editing operators (convert and delete active frame)

* Convert operator - can currently be used to convert active Grease Pencil layer to curves. I had a look at making this part of a special "curve sketching" macro, though it seems that we cannot have modal operators coming first in a macro (and also cannot specify operator calling modes)

* Delete Active Frame operator - does what its name say it does. It deletes the active frame for the active layer of Grease Pencil sketches.