PR #229 rebase

This is PR #229 rebased to fix the conflict.  The issue was just some whitespace changes in CellTracker, where surrounding lines were changed in later commits on the master branch.

I haven't done any review or testing, other than seeing that it builds.  If @Ueland knows how to rebase or merge with the master branch, it may be best to have him do it on the original PR (pushing to his fork's master branch should update the commits in the PR.)