MDEV-6247: Merge 10.0-galera to 10.1.

Merged lp:maria/maria-10.0-galera up to revision 3867.
Review fixes.
Fix Windows compiler errors.
Fix merge error.
Fix merge errors.
MDEV-6634: Wrong estimates for ref(const) and key IS NULL predicate

IS [NOT] NULL predicate is sargable within an outer join. Range
analysis only uses predicates from ON expressions, which have
regular semantics (without null-complemented rows, etc).
There is no reason not use IS [NOT] NULL predicates.
Merge lp:maria/maria-10.0-galera revisions 3867..3869 and
3871..3879.
MDEV-6305 - UNINIT_VAR emits code in non-debug builds

Reverted workaround for gcc bug, which was fixed 3 years ago:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772
Add missing test files for new configuration variables.

Added a new functions to handler API to forcefully abort_transaction,
producing fake_trx_id, get_checkpoint and set_checkpoint for XA. These
were added for future possiblity to add more storage engines that
could use galera replication.
MDEV-6634: Wrong estimates for ref(const): Update test result
MDEV-6247: Merge 10.0-galera to 10.1.

Merged lp:maria/maria-10.0-galera up to revision 3879.

Added a new functions to handler API to forcefully abort_transaction,
producing fake_trx_id, get_checkpoint and set_checkpoint for XA. These
were added for future possiblity to add more storage engines that
could use galera replication.
Merge branch 'bb-10.1-galera' of github.com:MariaDB/server into bb-10.1-galera
MDEV-6247: Merge 10.0-galera to 10.1.

    Merged lp:maria/maria-10.0-galera up to revision 3880.

    Added a new functions to handler API to forcefully abort_transaction,
    producing fake_trx_id, get_checkpoint and set_checkpoint for XA. These
    were added for future possiblity to add more storage engines that
    could use galera replication.
Fix compiler error when WITH_WSREP is not used.
Fix small error on LZMA compression error printout.
Move galera_sst_mode test to correct location. This test tests mysqldump
option.
Fix incorrect merge.
git: ignore errmsg.sys and typescript, better diff header for C/C++ files
Rule for configure wsrep-notify was missing.
Fix typo.