Fix rendering of negative numbers in columm layout

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/7008/
(cherry picked from commit 85d9e29e4b21b808a0599edb26fe37e6d5dae312)
Merge pull request #581 from gbehrmann/fix/2.8/rb7008

Fix/2.8/rb7008