Adds a new compile-time option MICROPY_PY_MATH_POW_FIX_NAN for use with
toolchains that don't handle pow-of-NaN correctly.

Prior to this commit, pow(-2, float('nan')) would return (nan+nanj), or
raise an exception on targets that don't support complex numbers.  This is
fixed to return simply nan, as CPython does.

Signed-off-by: Damien George <damien@micropython.org>

This is consistent with the other 'micro' modules and allows implementing
additional features in Python via e.g. micropython-lib's sys.

Note this is a breaking change (not backwards compatible) for ports which
do not enable weak links, as "import sys" must now be replaced with
"import usys".

Updating to Black v20.8b1 there are two changes that affect the code in
this repository:

- If there is a trailing comma in a list (eg [], () or function call) then
  that list is now written out with one line per element.  So remove such
  trailing commas where the list should stay on one line.

- Spaces at the start of """ doc strings are removed.

Signed-off-by: Damien George <damien@micropython.org>

So they can be skipped if __rOP__'s are not supported on the target.  Also
fix the typo in the complex_special_methods.py filename.

Signed-off-by: Damien George <damien@micropython.org>

This allows complex binary operations to fail gracefully with unsupported
operation rather than raising an exception, so that special methods work
correctly.

Signed-off-by: Damien George <damien@micropython.org>

Older implementations deal with infinity/negative zero incorrectly.  This
commit adds generic fixes that can be enabled by any port that needs them,
along with new tests cases.

For combinations of certain versions of glibc and gcc the definition of
fpclassify always takes float as argument instead of adapting itself to
float/double/long double as required by the C99 standard.  At the time of
writing this happens for instance for glibc 2.27 with gcc 7.5.0 when
compiled with -Os and glibc 3.0.7 with gcc 9.3.0.  When calling fpclassify
with double as argument, as in objint.c, this results in an implicit
narrowing conversion which is not really correct plus results in a warning
when compiled with -Wfloat-conversion.  So fix this by spelling out the
logic manually.

When the unix and windows ports use MICROPY_FLOAT_IMPL_FLOAT instead of
MICROPY_FLOAT_IMPL_DOUBLE, the test output has for example
complex(-0.15052, 0.34109) instead of the expected
complex(-0.15051, 0.34109).

Use one decimal place less for the output printing to fix this.

Since automatically formatting tests with black, we have lost one line of
code coverage.  This adds an explicit test to ensure we are testing the
case that is no longer covered implicitly.