entities for a non-BMP character on narrow build.

This is a belated backport of f7b47fb30169; Patch by Serhiy Storchaka.

members are integers.

getgroups(2) on OS X 10.8.  Original patch by Mateusz Lenik.

if Xcode command line tools were not installed.

The former block size traded away good fit within cache lines in
order to gain faster division in deque_item().  However, compilers
are getting smarter and can now replace the slow division operation
with a fast integer multiply and right shift.  Accordingly, it makes
sense to go back to a size that lets blocks neatly fill entire
cache-lines.

GCC-4.8 and CLANG 4.0 both compute "x // 62" with something
roughly equivalent to "x * 9520900167075897609 >> 69".

library has a package, lib-tk, that cannot be imported by normal means.
Lib/test/test_tk, etc, have special code to access this package.  I will not
bother with it unless the darwin check is needed before it gets moved to
test.(test-)support.py.

in the past and might be needed again in the future

(Consolidating this check and various checks in tkinter files and moving them
to test.support and test.regrtest will be another issue.)

Patch by Tshepang Lekhonkhobe.

(Consolidating this check and various checks in tkinter files and moving them
to test.support and test.regrtest will be another issue.)

Issue #18513: Add workaround for OS X 10.8 cexp bug that leads to wrong cmath.rect(0.0,-0.0) results.

(maxlen and weakref) to the end.