Fix suggested by Brett Wiren:

The test for "insideness" in TBox::DistancetoPrimitive in the case of
a filled TBox misses the TBox's very edge.  This causes 1 pixel
wide/tall TBoxes to be invisible to pointer interactions.


git-svn-id: http://root.cern.ch/svn/root/trunk@4306 27541ba8-7e3a-0410-8455-c3a389f83636