Plug : Rejig const_casts
Plug : Rejig const_casts

Move them closer to the culprit and document why they are necessary.

ImageEngine/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,hradec/gaffer,hradec/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,hradec/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,hradec/gaffer,hradec/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,GafferHQ/gaffer