On integrate-partial-getter branch: Fix partial getter implementation
for memcached-based caches (unused currently).

* subversion/libsvn_subr/cache-memcache.c
  (memcache_get_partial): adapt to changed build_key signature

Found by: Arnout van Meer <rr2do2{_AT_}splashdamage.com> 

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/integrate-partial-getter@1076552 13f79535-47bb-0310-9956-ffa450edef68