Looks like our Subversion repository got a bit corrupted today. Here's the instructions to restore, for future quick reference:
Subversion's repository database schema has changed occasionally during development. Old repositories, created with a pre-1.0 development version of Subversion, may require the following operation when upgrading. If a schema change happens between Subversion releases X and Y, then repository administrators upgrading to Y must do the following:
Shut down svnserve, Apache, and anything else that might be accessing the repository. All commands should be run as www user (sudo -u www)
% /usr/local/apache/bin/apachectl stop
% svnadmin dump /Library/Subversion > svndump.txt
% mv /Library/Subversion /Library/Subversion.borked
% svnadmin create /Library/Subversion
% svnadmin load /Library/Subversion < svndump.txt
% /usr/local/apache/bin/apachectl start