This change from the old int type to the real enum wxRasterOperationMode was missed during the fix of similar problems in r13403 (when similar fixes were applied), probably because ImageRoll and the affected variable are currently unused and the problem therefore doesn't cause a compilation error and is only fixed preventively.
Compatibility with wxWidgets 2.8 is assured thanks to a conditional definition of wxRasterOperationMode as int in ImageRoll.h, introduced in r13403.
We can't go to 3.0.1 yet as there are still build issues on
Linux and OSX. You can get Windows to build, but there's
still some display issues.
These changes should work with wxWidgets 2.8.12 as well, so
we can take our time to get things working properly before
switching over.