Issue is, when 'Rotate Aroud Selection' is set, in Edit mode we do a fake transform operation
to get center point around which to rotate. For curves, most transform operations involve
a check of handle types. For now, added 'TFM_DUMMY' as an exception here.
Think it would be best to actually undo those changes in case of cancelled operation,
but this is much more involved, while this fix is safe enough to be included in final 2.76.
cfc109eb92