For now just a todo list for a proposed new 'splitvertical' feature.

Initial patch by Christian Brabandt: http://groups.google.com/group/vim_dev/msg/7340b8005d1740d4

0. Write documentation for splitvertical, update interacting settings as we find them.

1. Update syntax files for [no|inv]spv and [no|inv]splitvertical

2. Add a :horizontal command

3. Trumps :set diffopt+='horizontal' right now; is this the right decision?