A fix and a test case for Bug#9643 " CURSOR_TYPE_SCROLLABLE dos not work"

- check on the client the unsupported feature and return 
an error message if it's been requested.
Additionally added API support for STMT_ATTR_PREFETCH_ROWS.
Post-review fixes.


include/errmsg.h:
  Add a new error code for "Not implemented" client-side error message.
include/mysql.h:
  Add a statement attribute STMT_ATTR_PREFETCH_ROWS - unsigned long
  number of rows to fetch per one COM_FETCH command, used when there
  is a read-only cursor.
  Note, that we don't break compatibility by adding this new member
  because MYSQL_STMT is always allocated inside the client library by
  mysql_stmt_init.
libmysql/errmsg.c:
  Text for the error message CR_NOT_IMPLEMENTED
libmysql/libmysql.c:
  Implement support for STMT_ATTR_PREFETCH_ROWS
  Return an error message on attempt to set an attribute of a prepared
  statement which is not implemented yet. We probably should be doing
  it in the server: currently the server just ignores unknown attributes.
tests/mysql_client_test.c:
  A test case for Bug#9643 "CURSOR_TYPE_SCROLLABLE dos not work"
  - check that an error message is returned for CURSOR_TYPE_SCROLLABLE.
  Additionally, check setting of STMT_ATTR_PREFETCH_ROWS.

include/mysql.h

@@ -663,6 +663,7 @@ typedef struct st_mysql_stmt
                                   unsigned char **row);
   unsigned long	 stmt_id;	       /* Id for prepared statement */
   unsigned long  flags;                /* i.e. type of cursor to open */
+  unsigned long  prefetch_rows;        /* number of rows per one COM_FETCH */
   /*
     Copied from mysql->server_status after execute/fetch to know
     server-side cursor status for this statement.
@@ -701,7 +702,12 @@ enum enum_stmt_attr_type
     unsigned long with combination of cursor flags (read only, for update,
     etc)
   */
-  STMT_ATTR_CURSOR_TYPE
+  STMT_ATTR_CURSOR_TYPE,
+  /*
+    Amount of rows to retrieve from server per one fetch if using cursors.
+    Accepts unsigned long attribute in the range 1 - ulong_max
+  */
+  STMT_ATTR_PREFETCH_ROWS
 };