fix refcount leak in LRU bump buf
fix refcount leak in LRU bump buf

takes a long time for mc-crusher to find this. I didn't run it long enough :(

gencer/memcached,bpzhang/memcached,gencer/memcached,dormando/memcached,guikcd/memcached,guikcd/memcached,guikcd/memcached,gencer/memcached,memcached/memcached,bpzhang/memcached,elfchief/memcached,dormando/memcached,elfchief/memcached,guikcd/memcached,memcached/memcached,memcached/memcached,dormando/memcached,gencer/memcached,guikcd/memcached,gencer/memcached,elfchief/memcached,dormando/memcached,bpzhang/memcached,elfchief/memcached,memcached/memcached,dormando/memcached,elfchief/memcached,bpzhang/memcached,memcached/memcached