Fix floating point issue in angle2(), acos(x) takes -1.0>= x <=1.0, but one point was calculating x to 1.00000000000000022204460, due to floating point impresision... Fix by rounding to 6 decimals.
Fix floating point issue in angle2(), acos(x) takes -1.0>= x <=1.0, but one point was calculating x to 1.00000000000000022204460, due to floating point impresision... Fix by rounding to 6 decimals.

TaipanRex/pyvisgraph,TaipanRex/visibility_graph