No need to check for result existence any more, store_result functions
now are shorter.
cli_read_binary_rows rewritten to handle MYSQL_DATA directly.


include/mysql.h:
  MYSQL_RES * pointer replaced with MYSQL_DATA: it saves us at least 2 mallocs
  per store_result and simplifies stored result handling.
  Plus it's done with cursor fetch in mind: cursor fetch will use this
  structure to buffer fetched rows.
libmysql/client_settings.h:
  signature of cli_read_binary_rows changed
libmysql/libmysql.c:
  MYSQL_DATA is now used to handle result.
  cli_read_binary_rows rewritten to use MYSQL_DATA directly.
libmysql/libmysql.def:
  declarations of new calls in the library
libmysqld/lib_sql.cc:
  MYSQL_DATA is now used to handle result.
  cli_read_binary_rows rewritten to use MYSQL_DATA directly.