dot error if icons not set

[Jesper Saxtorph]

dot is looking for the file htdocs/images/none if an icon is not set.

I fixed it by adding and png called none to: projectplanplugin/0.11/trunk/projectplan/htdocs/images/ then adding the line: u'images': u'none', to the "htdocsubdirmapping = {" section of setup.py

After doing "python setup.py bdist_egg" everything seems to work as dot can find the file none and show that when nothing is defined.

This behaviour was observed on an Ubuntu 12.04 with the standard ubuntu packages for dot 2.26.3 and trac 0.12. ProjectPlan was downloaded from the projectplan wiki download link and gave me r12566