[ctioga2] (simple) format specification for the ticks labels on a given axis

git-svn-id: svn+ssh://rubyforge.org/var/svn/ctioga2/trunk/ctioga2@482 86c91514-0d3b-42e0-aed1-4dfce116d947
[ctioga2] manually specify the background lines positions

git-svn-id: svn+ssh://rubyforge.org/var/svn/ctioga2/trunk/ctioga2@483 86c91514-0d3b-42e0-aed1-4dfce116d947