Consider mouse sensor at the bot tail

[GoogleCodeExporter]

The position could additionally estimated by a mouse sensor on the tail of the 
bot.

The sensor probably shouldn't be directly measuring the ground because of 
problems on non flat surfaces, but maybe indirectly e. g.: Use a free rotating 
ball and measure the movement and direction of the ball

Original issue reported on code.google.com by [email protected] on 23 Jan 2013 at 9:08