Why does mod_dav_svn complain about a bad database version when I start Apache? It found db-3.X, rather than db-4.X.

Your apr-util linked against DB-3, and svn linked against DB-4. Unfortunately, the DB symbols aren't different.

When mod_dav_svn is loaded into Apache's process-space, it ends up resolving the symbol names against apr-util's DB-3 library. The solution is to make sure apr-util compiles against DB-4. You can do this by passing specific switches to either apr-util's or apache's configure: "--with-dbm=db4 --with-berkeley-db=/the/db/prefix".