lmdb-backend: conditionally support config for 'lifo' and 'coalesce' envflags;
 ! conditionally enforce MDB_LIFORECLAIM & MDB_COALESCE (this MUST be remove from the release);
 ! only test-060 (this crunch MUST be remove later);
 ! engage all tests (not only test-060, this crunch MUST be remove later);
 lmdb: MDB_LIFORECLAIM & MDB_COALESCE modes;