This command was used:
find . -type f -print0 | xargs -0 sed -i 's/return undef/return/g'
The idea behind this commit is described on http://oddmuse.org/wiki/Refactoring page.
In short: 'return undef' returns (undef) in list context (a list with one element),
which is wrong.
Replaced the $Id$ tags in $WikiDescription for all the modules and wiki.pl itself with a link to the source and an appropriate wiki page, if possible. This is shown in action=version and should help users figure out what another wiki has installed.
