Fix complex math computations.

There are still outstanding special values, such as Inf, -Inf, NaN,
and -0.0, as well as subnormal values, to be considered in some of the
functions, as seen in test_cmath.test_specific_values.

In addition, transcendental function precision is not as high as seen
in CPython. We should revisit by incorporating Apache Common Math's
FastMath implementation, but the overall jar is too big for us to
directly incorporate.

Partial fix of http://bugs.jython.org/issue1861 - remove skip FIXMEs
in tests.