Use less aggressive conversion to exceptions, in particular
do not convert warnings that happen during check_liveness. If the
server has gone away this will just reconnect and we still end up
with a valid connection, so it shouldn't throw.
Also drop some unnecessary checks for malloc returning NULL.
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.
