ellipticcurve.Point.double: check for INFINITY, suggested by Dcoder.
ellipticcurve.Point.double: check for INFINITY, suggested by Dcoder.

arnuschky/python-ecdsa,cornelinux/python-ecdsa,alex/python-ecdsa,GreatFruitOmsk/python-ecdsa,romanz/python-ecdsa