patch for (global level, png format) gantt export problem on 0.8 branch
same bug on trunk is fixed by r2332. but I think we need backport patch to 0.8 branch. (because I use it, maybe not only me.)
slightly different way, I use a new variable named basename. because there are two of same routine (that checking project.nil), it brings mistake/missing.
please check the patch. thanks.