Fixes a bug where splitting then moving in the other orientation
(e.g. v-splitting and moving right) would result in the old
indicators not disappearing.
Due to lots of cases which were added and added to tree_move(), the function
was not really easy to understand. For this refactoring, I wrote tree_move()
from scratch, thinking about (hopefully) all cases. The testsuite still passes.
The move command also has different parameters now. Instead of the hard to
understand 'before v' stuff, we use 'move [left|right|up|down]'.
Fernando Tarlá Cardoso Lemos