Add code to speed up Math::BigFloat->batan(). Thanks to DANAJ (Dana
Jacobsen) for the patch.Re-write Math::BigFloat->batan2() completely, except for the parts related
to the rounding. The old version was sometimes correct, sometimes off by pi,
and sometimes very inaccurate. Also add more tests.Make it clearer in Math::BigFloat->bpi() when it is called as a method vs.
as a function.The Math::BigFloat->bpi() method can now be used as an instance method to
assign pi to $x, as in $x->bpi().Add tests for as_oct().
Minor simplifications in Math::BigInt->as_oct() and
Math::BigInt::Calc::_as_oct().