SF bug 115831 and Ping's SF patch 101751, 0.0**-2.0 returns inf rather than

SF bug 115831 and Ping's SF patch 101751, 0.0**-2.0 returns inf rather than
raise ValueError.  Checked in the patch as far as it went, but also changed
all of ints, longs and floats to raise ZeroDivisionError instead when raising
0 to a negative number.  This is what 754-inspired stds require, as the "true
result" is an infinity obtained from finite operands, i.e. it's a singularity.
Also changed float pow to not be so timid about using its square-and-multiply
algorithm.  Note that what math.pow does is unrelated to what builtin pow
does, and will still vary by platform.