debian apt-get install trac 0.12

do this

sudo apt-get install trac

at this point you will install only  trac 0.11

then download Trac-0.12.3.tar.gz

tar -xpzvvf Trac-0.12.3.tar.gz

cd Trac-0.12.3

sudo easy_install Genshi

sudo python ./setup.py install

then finally a successful build of trac 0.12 on debian 5.0/6.0