ENH: consistent reverse iterator definitions for UList and FixedList
- consistent with C++ STL conventions, the reverse iterators should use operator++ to transit the list from rbegin() to rend(). The previous implementation used raw pointers, which meant that they had the opposite behaviour: operator-- to transit from rbegin() to rend(). The updated version only has operator++ defined, thus the compiler should catch any possible instances where people were using the old (incorrect) versions. - updated forAllReverseIters() and forAllConstReverseIters() macros to be consistent with new implementation and with C++ STL conventions.