- Add mysqlnd support for PDO_mysql, fixes at least bug#41997,#42499,

- Add mysqlnd support for PDO_mysql, fixes at least bug#41997,#42499,
  pecl#12794, pecl#12401

# Running the tests:
# (Note: Doesn't work currnetly on HEAD, see:
#  http://news.php.net/php.qa/64378)
#
#  PDO_MYSQL_TEST_DSN  - DSN
#    For example: mysql:dbname=test;host=localhost;port=3306
#
#  PDO_MYSQL_TEST_HOST    - database host
#  PDO_MYSQL_TEST_DB      - database (schema) name
#  PDO_MYSQL_TEST_SOCKET  - database server socket
#  PDO_MYSQL_TEST_ENGINE  - storage engine to use
#  PDO_MYSQL_TEST_USER    - database user
#  PDO_MYSQL_TEST_PASS    - database user password
#  PDO_MYSQL_TEST_CHARSET - database charset
#
#  NOTE: if any of PDO_MYSQL_TEST_[HOST|DB|SOCKET|ENGINE|CHARSET] is
#  part of PDO_MYSQL_TEST_DSN, the values must match. That is, for example,
#  for PDO_MYSQL_TEST_DSN = mysql:dbname=test you MUST set PDO_MYSQL_TEST_DB=test.