10.1 introduced a problem:
Execution time for various recursive stages
(walk, update_used_table, and propagate_equal_fields)
in NULLIF is O(recursion_level^2), because complexity is
doubled on every recursion level when we copy args[0] to args[2].

This change fixes to avoid unnecessary recursion in:
- Item_func_nullif::walk
- Item_func_nullif::update_used_tables
- Item_func_nullif::propagate_equal_fields
when possible.

         CREATE function.

         Test case added.

take MDL_SHARED_WRITE instead of MDL_SHARED_NO_READ_WRITE
for OPTIMIZE TABLE. For engines that need a stronger
lock (like MyISAM), reopen the table with
MDL_SHARED_NO_READ_WRITE.

Two bugs here:
* the server could create an frm (with a long attribute
  value) that it could not read back
* Connect engine opened files from inside DROP TABLE
  and was ignoring the error (correctly) but was not
  hiding it from the server (incorrectly). This caused
  a crash later when DROP TABLE was finishing successfully
  while stmt_da already have seen an error.

Also added a text case for
  MDEV-7935 CREATE TABLE ... AS SELECT ... can cause a Server crash (Assertion `0' in Protocol::end_statement)
because Connect stopped clearing the error status
in stmt_da as a fix for MDEV-7935

* my_yyabort_error() helper
* s/lex->thd/thd/
* remove 'else' after MYSQL_YYABORT (for consistency,
  95% of the parser did not use 'else' in this case)
* simplify ER_SLAVE_HEARTBEAT_VALUE_OUT_OF_RANGE

when reading table options

install private generated files

Do not mark subquery as inexpensive when it is not optimized.

        Compiler there is strict about the C/C++ call model
        mixing in function variable assumptions.
        Fixed by adding some 'extern "C"' and changing
        '?' operator with 'if'.

MySQL 5.6 do not work with MariaDB 10.1

Analysis: Problem is that tablespace flags bit DATA_DIR
is on different position on MySQL 5.6 compared to
MariaDB 10.1.

Fix: If we detect that there is difference between dictionary
flags and tablespace flags we remove DATA_DIR flag and compare
again. Remote tablespace is tried to locate even in case
when DATA_DIR flag is not set.

otherwise the plugin does not get compiled if
cmake is called multiple times.

        The check_user_can_set_role() used find_user_exact() to get the
        permissions for the SET ROLE NONE command. Which returned NULL too often,
        for instance when user authenticated as 'user'@'%'.
        Now we use find_user_wild() instead.

Added mysql_to_mariadb.sql script, to change mysql.user tables from
MySQL 5.7 to MariaDB.
After this script is run, one can get the other tables fixed by running
mysql_upgrade

Analysis: When pages in doublewrite buffer are analyzed compressed
pages do not have correct checksum.

Fix: Decompress page before checksum is compared. If decompression
fails we still check checksum and corrupted pages are found.
If decompression succeeds, page now contains the original
checksum.

Clang warns on this code because it is memsetting over a vtable contained in a
struct in the best_positions array. The diagnostic text is:

mariadb/sql/sql_select.cc:24462:10: error: destination for this 'memset' call is
a pointer to class containing a dynamic class 'Duplicate_weedout_picker'; vtable
pointer will be overwritten [-Werror,-Wdynamic-class-memaccess]
  memset(best_positions, 0, sizeof(POSITION) * (table_count + 1));
  ~~~~~~ ^

Patch contributed by David Gow.

MariaDB 10.1.x 32-bit binaries.

Problem was the fact that tablespace size was incorrectly
rounded to next extent size (1M).

wrong mutex usage from safe_mutex.
Ensure that LOCK_status is always taken before LOCK_thread_count

Problem was that cost_group_min_max() could not handle if group by was optimized away.

MDEV-9884: Existing /var/lib/mysql/.sst directory (with contents) causes SST to fail with xtrabackup-v2

[Fix taken from https://github.com/percona/percona-xtradb-
cluster/commit/b3ee75949ed82b88f355ca2e26431350cc1c89ac]

During SST, the receiver node creates .sst directory under
datadir to process/prepare the received data and removes it
at the end of the process. In case of error, this directory,
however, was not removed, which later caused subsequent SSTs
to fail. Fixed by removing this directory at the beginning
of SST if it existed.

as it fails on new builders.

msxml6 is found on all Windows we support, thus there is no reason to
search for it.