When using a parameter bind MYSQL_TYPE_DATE in a prepared statement,
the time part of the MYSQL_TIME buffer was written to zero in
mysql_stmt_execute(). The param_store_date() function in libmysql.c
worked directly on the provided buffer.
Changed to use a copy of the buffer.


libmysql/libmysql.c:
  fix for bug #20152
tests/mysql_client_test.c:
  added test for bug#20152