modify aStar path generation and retrieval by vyo on 3/11/2013

Add support for taking into accout diagonal movement during
path finding.
Also added support for diagonal movement during the backtracking
phase.
Added a simplified version of the TwoNorm - it it calculates the
distance as indicated by the OneNorm, i.e. the sum of the
differences in each coordinate pair, and then subracts the bigger
of the two multiplied by factor 0.7. This is to enable diagonal
movement without needing to compute squares and square roots.