Handle moving between windows as if a focus event occured

When a window is no longer active, we want absoulte instead
of relative line numbering...

Signed-off-by: Greg Dietsche <Gregory.Dietsche@cuw.edu>
Merge pull request #13 from dietsche/f3ed5b38f784f8035cd2b82367e3069a9745a0ca

Toggle line numbers correctly when switching windows