Change {history}.nid to an unsigned int in order to match {node}.nid.
function node_update_7016() {
db_drop_primary_key('history');
db_drop_index('history', 'nid');
db_change_field('history', 'nid', 'nid', array(
'description' => 'The {node}.nid that was read.',
'type' => 'int',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
));
db_add_primary_key('history', array(
'uid',
'nid',
));
db_add_index('history', 'nid', array(
'nid',
));
}