By default trac uses sqlite for its database backend. However, when emerging trac, the its sqlite USE flag is off by default, which causes trac-admin script to fail if pysqlite is not installed. Although trac can use postgresql or mysql instead of sqlite, since by default trac's scripts assume sqlite, I think would make sense to install trac with pysqlite unless the user has -sqlite in USE flags.
Except that we can't do it now.
