See that branch's log for full details, but in short:
The branch rewrote various in-memory caches in FSFS to use a unified API. By default this API is implemented by some in-process hashes, but via a configuration file (db/fsfs.conf), it can use memcached instead. Additionally, expanded fulltexts are cached if memcached is available.
memcached is accessed with the apr_memcached API, which will be in a future version (1.3.x branch, now) of apr-util, and is also available as an separately-distributed library. The build system knows how to deal with both.
Other things that changed:
* The test suite now has a config file; currently, the config file is just used as the FSFS config file for any created repositories.
* New random APIs: svn_base64_encode_string2, svn_stream_from_string.
* ra_local ignores "FS warnings" instead of aborting.