- The background grid on lego and surface plots is now aligned on the
   axis main tick marks. It works for optimised and none optimised axis
   divisions.

 - It is now possible to have non optimised axis divisions (number of
   divisions less than 0) on all 3D plots (lego and surfaces) axis and on
   the colour palette axis.

Olivier


git-svn-id: http://root.cern.ch/svn/root/trunk@4216 27541ba8-7e3a-0410-8455-c3a389f83636