Moved proxy caching to overlay

servers/slapd/back-meta/Makefile.in

servers/slapd/back-meta/back-meta.h

servers/slapd/back-meta/cache-config.c

servers/slapd/back-meta/cache-merge.c

servers/slapd/back-meta/cache-query.c

servers/slapd/back-meta/cache-remove.c

servers/slapd/back-meta/cache-search.c

servers/slapd/back-meta/cache-substring.c

servers/slapd/back-meta/cache-template.c

servers/slapd/back-meta/cache.h

servers/slapd/back-meta/config.c

servers/slapd/back-meta/init.c

servers/slapd/back-meta/search.c