Add errno() and error() methods (issue #5).
Add errno() and error() methods (issue #5).

beni55/node-mysql-libmysqlclient,beni55/node-mysql-libmysqlclient,Sannis/node-mysql-libmysqlclient,beni55/node-mysql-libmysqlclient,Sannis/node-mysql-libmysqlclient,Sannis/node-mysql-libmysqlclient,beni55/node-mysql-libmysqlclient,beni55/node-mysql-libmysqlclient,Sannis/node-mysql-libmysqlclient