Implemented Martin's suggestion to clear the free lists during the garbage collection of the highest generation.

when trying to remove a pid that in not in the activechildren list.

self._numerator and self._denominator. This speeds abs() up from 12.2us to
10.8us and trunc() from 2.07us to 1.11us. This doesn't change _add and friends
because they're more complicated.

  ./python.exe -m timeit -s 'from fractions import Fraction' 'Fraction(3)`
31.7 usec/loop -> 9.2 usec/loop

  ./python.exe -m timeit -s 'from fractions import Fraction' 'Fraction(3, 2)'`
27.7 usec/loop -> 9.32 usec/loop

  ./python.exe -m timeit -s 'from fractions import Fraction; f = Fraction(3, 2)' 'Fraction(f)'
31.9 usec/loop -> 14.3 usec/loop

works.

Thanks to Jeroen Ruigrok van der Werven for the fix.

  ./python.exe -m timeit -s 'from fractions import Fraction; f = Fraction(3, 2)' 'isinstance(3, Fraction); isinstance(f, Fraction)'
from 12.3 usec/loop to 3.44 usec/loop and
  ./python.exe -m timeit -s 'from fractions import Fraction' 'Fraction(3, 2)'
from 48.8 usec to 23.6 usec by avoiding genexps and sets in __instancecheck__
and inlining the common case from __subclasscheck__.

result on Windows.

test_fractions.py.  This should have been part of the name
change from Rational to Fraction.

classmethods instead of staticmethods.

Remove Fraction.to_continued_fraction and
Fraction.from_continued_fraction

implements the chunked encoding incorrectly.
Will backport to 2.5.

Fraction(1, 2) instead of Fraction(1,2).

with numbers.Rational.  See issue #1682 for related discussion.