extend the fix from 5.5 (in read_sep_field()) to apply to read_xml_field()

Actual error number returned from the query depends what point
corrupted page is accessed, is it accessed when we read
one of the pages for result set or is it accessed during
background page read.

Removed creation of unused backup file and unused variables.

Problem was two race condtion in Aria page cache:
- find_block() didn't inform free_block() that it had released requests
- free_block() didn't handle pinned blocks, which could happen if
  free_block() was called as part of flush. This is fixed by not freeing
  blocks that are pinned.  This is safe as when maria_close() is called
  when last thread is using a table, there can be no pinned blocks. For
  other flush calls it's safe to ignore pinned blocks.

- Changed to 'strict'
- Fixed scope of variables
- Made timing smaller for of repair, check, flush and alter to get them to
  trigger earlier

In MariaDB Server before 10.2, InnoDB will not be shut down properly
if startup fails. So, Valgrind failures are to be expected.
Disable the test under Valgrind. In 10.2, it should pass with Valgrind.

This patch corrects the fix for the bug mdev-10693.
It is critical for the function get_best_combination() not to call
create_ref_for_key() for constant tables.
This bug could manifest itself only in multi-table subqueries where
one of the tables is accessed by a constant primary key.

otherwise make didn't know it needs to regenerate lex_hash.h
when gen_lex_hash (that is sql_yacc.h, that is sql_yacc.yy) changes.

MDEV-12522: mysqltest replace regex +  sys_vars.sysvars_wsrep test to be version independent

MDEV-12646: wsrep_new_cluster: Add -h and --help options

Remove compile warning - "this" canot be null

This regression was caused by MDEV-12467 encryption.create_or_replace
hangs during DROP TABLE, where if table->is_stopping() (i.e. when
tablespace is dropped) background key rotation thread calls
fil_crypt_complete_rotate_space to release space and stop rotation.
However, that function does not decrease number of rotating
threads if table->is_stopping() is true.

/home/travis/build/MariaDB/server/extra/mysqld_safe_helper.c:62:21: warning: too many arguments in call to 'do_usage'
    do_usage(argv[0]);
    ~~~~~~~~        ^
1 warning generated.

From: https://github.com/devexp-db/mariadb/blob/f27/mariadb-galera-new-cluster-help.patch

/home/travis/build/MariaDB/server/sql/sql_class.cc:1941:15: warning: 'this' pointer cannot be null in well-defined C++ code; pointer may be assumed to always convert to true [-Wundefined-bool-conversion]
          if (this && WSREP(this) && wsrep_thd_is_BF(this, FALSE))
              ^~~~ ~~

|| kv >= crypt_data->min_key_version,
encryption.innodb_encryption_tables failed in buildbot.

Now that key_version is not stored when page is read to
buf_page_t::key_version but always read from actual page
this assertion is not always valid.

This fixes a regression caused by MDEV-12428.
When we introduced a variant of fil_space_acquire() that could
increment space->n_pending_ops after space->stop_new_ops was set,
the logic of fil_check_pending_operations() was broken.

fil_space_t::n_pending_ios: A new field to track read or write
access from the buffer pool routines immediately before a block
write or after a block read in the file system.

fil_space_acquire_for_io(), fil_space_release_for_io(): Similar
to fil_space_acquire_silent() and fil_space_release(), but
modify fil_space_t::n_pending_ios instead of fil_space_t::n_pending_ops.

Adjust a number of places accordingly, and remove some redundant
tablespace lookups.

The following parts of this fix differ from the 10.2 version of this fix:

buf_page_get_corrupt(): Add a tablespace parameter.

In 10.2, we already had a two-phase process of freeing fil_space objects
(first, fil_space_detach(), then release fil_system->mutex, and finally
free the fil_space and fil_node objects).

fil_space_free_and_mutex_exit(): Renamed from fil_space_free().
Detach the tablespace from the fil_system cache, release the
fil_system->mutex, and then wait for space->n_pending_ios to reach 0,
to avoid accessing freed data in a concurrent thread.
During the wait, future calls to fil_space_acquire_for_io() will
not find this tablespace, and the count can only be decremented to 0,
at which point it is safe to free the objects.

fil_node_free_part1(), fil_node_free_part2(): Refactored from
fil_node_free().

innodb calls sd_notify(), it must be linked with libsystemd

use X509_check_host for OpenSSL 1.0.2+
This adds:
* support for subjectAltNames
* wildcards
* sub-domain matching

magic--

and make sure that private ca key is not deleted at the end of
the procedure, so that we could generate additional certificates
any time without regenerating everything

use --defaults-file to avoid reading ~/.my.cnf
and don't crash if some ibdata file couldn't be opened

incremental prepare is running.