Use forward rangefinders in get error functions

[QuentinTorg]

If the left and right rangefinders don't see walls then use the forward rangefinders to push away from the nearest wall. We can probably use the identical error return function as for diagonals because this function just saves us from extreme errors.

We could also use this if we make our search turn profiles smaller radius and add a forward move before the turn starts and after it ends. The forward move could have a function that compares right and left forward readings and makes sure they match so that turns are always entered square to the opposing wall if it exists