MDEV-5811: Server crashes in best_access_path with materialization+semijoin and big_tables=ON
- With big_tables=ON, materialized table will use Aria (or MyISAM) SE, which
  allows prefix key reads. However, the temp.table has rec_per_key=NULL which
  causes the optimizer to crash when attempting to read index statistics for a 
  prefix index read.
- Fixed by providing a rec_per_key array with zeros (i.e. "no statistics data")
Merge
MDEV-5862 server_audit test fails in buildbot on Mac (labrador).
        The RTLD_DEFAULT value on Labrador machine is not NULL,
        so the dlsym() commands in the server_audit just fail
        to bind the necessary functions.
        Fixed by using RTLD_DEFAULT explicitly.
MDEV-5892 Centos startup script is broken

Don't try to be smart about --socket.
Assume that if user has set up a non-standard location for a socket,
she did it consistently for both a server and clients
(otherwise most clients won't work anyway).
MDEV-5773 symbol list_add, version libmysqlclient_18 not defined in file libmysqlclient.so.18 with link time reference
MDEV-5763 libmyodbc.so: undefined symbol: int2str
MDEV-5739 Symbol missing in libmysqlclient.so.18 (make_scrambled_password)

pam_mysql and especially myodbc need tons of internal symbols on Debian, argh!
Fix to make it compiling with valgrind.
MDEV-5783 Assertion `0' failed in make_sortkey(SORTPARAM*, uchar*, uchar*) on ORDER BY HEX( UNCOMPRESSED_LENGTH( pk ) )
MDEV-5831 Upgrade from MariaDB 5.5.36 via yum fails

Allow "rpm -q --whatprovides mysql-server" to return more than one row.
(all rows should be identical though)
rpl tests: move "include/master-slave.inc" down to be after all possible
checks that can skip the test
tokudb: make compression=TOKUDB_ZLIB the default (instead of TOKUDB_UNCOMPRESSED)
for new tables
MDEV-5822 TokuDB fails to compile without partition storage engine
mysqltest bug: reset --replace command after every
error message (because error messages use replacements)
MDEV-5913 Windows: 10.0 crashes on shutdown

add pthread_mutex_destroy(&THR_LOCK_dbug); that was apparently
forgotten since the very first MySQL version
5.3 merge
don't put libmysqlclient symbols extra-used on debian
in the libmysqlclient_16 version node.
move file->position() down, to make sure it's executed only when
previous file->index_next (or other file->... index access method)
succeeded