Directory, Proxy and Location - how to co-exist in one Apache configuration?
Add:
ProxyPass /trac !
before ProxyPass for '/'.
See:
http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#proxypass
You are also missing a WSGIProcessGroup directive. That Trac instance isn't going to run in the daemon mode process you created. See:
http://code.google.com/p/modwsgi/wiki/IntegrationWithTrac