Just use memalign, not posix_memalign

Everything has it. Solaris doesn't have posix_memalign.
ITS#7917 fix mdb_dbi_open

Don't let dummy go out of scope
ITS#7917
Merge remote-tracking branch 'origin/mdb.master' into OPENLDAP_REL_ENG_2_5
ITS#7906 more cleanup

db_open/close were not symmetric with init/destroy
ITS#7919 fix cache DB config

Don't accept config directives for cache DB until the cache backend type
has been set.
ITS#7838 fix typos in prev commit
ITS#7920 fix for slapacl

This needs to be streamlined in 2.5, current tool API is a mess.
Note that tools need streamlining in 2.5