PISMIcebergRemover should not remove SSA B.C. cells.
Update examples/piktests/flowline/.
Fix #115. Needs testing.

This commit uses a version of the code by @matthiasmengel, see
<https://github.com/pism/pism/issues/115#issuecomment-11613119>.
Re-implements "-float_kill". Needs testing.
Remove unused IceModel members.