OSYSTEM: Reverts reverse_iterator to a sibling of iterator rather than a
wrapper. Fixes small bugs in the reverse_iterator implemention.

While having reverse_iterator as a wrapper over an iterator allowed for
nice mutation opportunities, it made the logic annoying and for
reverse_begin / reverse_end was going to require dynamic memory. Also, in
normal use, a reverse_iterator is going to be created from Common::list
functions rather than actually reversing an iterator.
I added the python command in-front of the python file in the makefile.
msys complained otherwise.