I checked and this appears to be a packaging issue in the debian. The original trac tarball doesn't include any reference to that, but trac_0.11.7-3.diff does around line 1024, and that version fails to install on a fresh 10.04 system with the same error you described. 0.11.7-1 is unaffected.
The Debian bug 576988 was opened, but they say should have been fixed in 0.11.7-3 (and I double-checked, the ubuntu 0.11.7-3 is the same as the debian one). I don't have a Debian machine handy to test whether 0.11.7-3 installs ok on debian.
I checked and this appears to be a packaging issue in the debian. The original trac tarball doesn't include any reference to that, but trac_0.11.7-3.diff does around line 1024, and that version fails to install on a fresh 10.04 system with the same error you described. 0.11.7-1 is unaffected.
The Debian bug 576988 was opened, but they say should have been fixed in 0.11.7-3 (and I double-checked, the ubuntu 0.11.7-3 is the same as the debian one). I don't have a Debian machine handy to test whether 0.11.7-3 installs ok on debian.