A donor node does a flush tables and then tries to
freeze innodb writes before proceeding with SST.
However, innodb_disallow_writes was missing in xtradb.
Merged 'InnodbFreeze' patch from maria-5.5-galera's to
xtradb. Also, merged some changes missing in innobase's
os0file.cc.

Added a basic test case for innodb_disallow_writes system
variable.

https://bugs.launchpad.net/percona-xtradb-cluster/+bug/1314854

Some wsrep system variables contain uppercase letters in
their names, as a result of which they seemed out of order
after sorting. Fixed by using case-insensitive string
comparison function to perform sorting.

state to the joiner

In mysqldump SST, if Galera nodes are started with --log-bin and
-log-slave-updates, the GTID sequence increases as the dump is
played on the joiner, leaving behind the donor.

This patch introduces a new mysqldump option --galera-sst-mode,
which if enabled, would

a) Add command to set off binary logging (log_bin=OFF).
b) Add command to set @@global.gtid_binlog_state to that
   of donor.

This will help in keeping the GTIDs consistent post-SST across
the nodes.

  Some variables weren't cleared properly so consequitive embedded server start/stop failed.
  Cleanups added. Also mysql_client_test.c extended to test that (taken from Mattias Johnson's patch)

When plugin=mysql_native_password (or mysql_old_password) take the password
from *either* password *or* authentication_string, whichever is set.
This makes no sense, but alas, that's what MySQL-5.6 does.

fix for ranges like "indexed_datetime OP time"
(test case is in the previous revision)

fix for ref like "indexed_time = datetime"

from 10.0:r4231).

(prep for MDEV-6065)

The method JOIN_CACHE::init may fail (return 1) if some conditions on the
used join buffer is not satisfied. For example it fails if join_buffer_size
is greater than join_buffer_space_limit. The conditions should be checked
when running the EXPLAIN command for the query. That's why the method
JOIN_CACHE::init has to be called for EXPLAIN commands as well.

MDEV-4440 IF NOT EXISTS in multi-action ALTER does not work when the problem is created by a previous part of the ALTER.
        Loops added to the handle_if_exists_option() to check the
        CREATE/DROP lists for duplicates.

Part#1. 

table_cond_selectivity() should discount selectivity of table' 
conditions only when ity counts that selectivity to begin with. 

For non-ref-based access methods (ALL/range/index_merge/etc),
we start with sel=1.0 and hence do not need to discount any
selectivities.