svn 1.7.8 database is locked, cannot release

This helped me solve the problem (subversion 1.7.10):

$ cd /my/repository/.svn
$ mv wc.db wc.db.old
$ sqlite3 wc.db.old
sqlite> .backup main wc.db
sqlite> .exit

After making sure it works, you can remove wc.db.old.

See also: http://technosophos.com/content/sqlite-database-locked-error-and-unlocking-database