(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.

- In table_cond_selectivity(), reset keyuse variable between the loops.

- Key_value_records_iterator::get_next() should pass pointer to the key 
  to handler->ha_index_next_same().  Because of a typo bug, pointer-to-pointer
  was passed instead in certain cases.

MDEV-6101 Hybrid functions do not add CURRENT_DATE when converting TIME to DATETIME

- When range optimizer cannot the lookup value into [VAR]CHAR(n) column,
  it should produce:
  = "Impossible range" for equality
  = "no range" for non-equalities.

replace another old "was there a filesort?" test with
a correct "did filesort calculate found_rows?" test.

simplify test case for MDEV-5898

MDEV-5998 MySQL Bug#11756966 - 48958: STORED PROCEDURES CAN BE LEVERAGED TO BYPASS DATABASE SECURITY

Merge from mysql-5.6:
revno: 3257
committer: Jon Olav Hauglid <jon.hauglid@oracle.com>
branch nick: mysql-trunk-bug11756966
timestamp: Thu 2011-07-14 09:32:01 +0200
message:
  Bug#11756966 - 48958: STORED PROCEDURES CAN BE LEVERAGED TO BYPASS
                 DATABASE SECURITY

  The problem was that CREATE PROCEDURE/FUCTION could be used to
  check the existence of databases for which the user had no
  privileges and therefore should not be allowed to see.

  The reason was that existence of a given database was checked
  before privileges. So trying to create a stored routine in
  a non-existent database would give a different error than trying
  to create a stored routine in a restricted database.

  This patch fixes the problem by changing the order of the checks
  for CREATE PROCEDURE/FUNCTION so that privileges are checked first.
  This means that trying to create a stored routine in a
  non-existent database and in a restricted database both will
  give ER_DBACCESS_DENIED_ERROR error.

  Test case added to grant.test.

when the bundled pcre is used, install its pcre.h in mysql/private/

don't use the default storage engine for mysql.gtid_slave_pos, prefer innodb.
but alter it to myisam in mtr, because many tests run without innodb.

don't use the interval timer when absolute time values are needed

"have_warnings" was set to an uninialized value when converting
a negative number to datetime.