# unpack with;
$ tar xvzf albackup.tgz
# Use rsync 2.6.6 (or earlier versions);
$ rsync -azv --cvs-exclude mediawiki-1.5.3 newdir
# Note that newdir/mediawiki-1.5.3/ does *not* contain LocalSettings.php
# This is an error if I read the default_cvsignore array of rsync-2.6.6/exclude.c correctly.
--cvs-ignore ignores both that laundry list in exclude.c and any additional files specified in per-directory .cvsignore files. I downloaded the package you linked and found that the MediaWiki people listed LocalSettings.php in .cvsignore, so rsync's behavior is correct. A "sufficiently empowered user" should resolve this bug invalid--why does Bugzilla let me click on things I'm not allowed to actually do?
Matt has the solution - the mediawiki guys has entered the missing files into .cvsignore, which rsync correctly parses and thus ignores LocalSettings.php.
Nasty problem, but this is not an error in rsync!