Fix some of the C++ highlighting rules

- Fix some rules: remove 'fro', change 'reinterpret-cast' to 'reinterpret_cast'
- Use an updated set of rules based on C++11 keywords (e.g. http://en.cppreference.com/w/cpp/keyword) (but, maybe this should wait until C++0x is truly supported by R / CRAN?)
- Reorder keywords alphabetically