back-mdb: stack backtrace on SIGSEGV and friends.
back-mdb: stack backtrace enabled only if symbols available.
syncrepl: ANY-logging for delete-ops.
syncrepl: ANY-logging for REFRESH.
 ! debugging crutchs, MUST be removed before release.

   LY_DEBUG;
   conditionally enforce MDB_LIFORECLAIM & MDB_COALESCE;
   test pattern hack (this crunch MUST be remove later);
   asserts for check reclaimable;
   inject SIGSERV on 42th checkpoint;
   added Yota's lmdb-tests;
+ void mdb_showinfo(MDB_env *env, int rdrinfo, int freinfo)