pseudo-random number generator on fork().

100 headers are read.  Adapted from patch by Jyrki Pulliainen.

prevent readline() calls from consuming too much memory.  Patch by Jyrki
Pulliainen.

prevent readline() calls from consuming too much memory.  Patch by Jyrki
Pulliainen.

for security reasons.  It now doesn't match multiple wildcards nor wildcards
inside IDN fragments.

line length.  Patch by Emil Lind.

This mitigates the current Aqua Tk refresh problem on OS X 10.9
by backporting 2.7.x behavior and is transparent to the user.

- cross-references and attributions for inspect changes
- note improvements to inspect and pydoc handling of
  metaclasses and dynamic attributes (courtesy of the
  enum PEP)
- group all CPython implementation specific changes
  into a common section
- add see also links for most of the PEPs
- fix the see also link for the release PEP
- add suitable caveats on Argument Clinic inclusion
- clarify the change to __wrapped__ handling

Make it easier for users to make use of the backup _tkinter linked
with the third-party Tcl and Tk frameworks in /Library/Frameworks.
The two tkinter variants are now installed in separate directories
under a new lib-tkinter.  This allows per-user selection by
manipulating sys.path, directly or with PYTHONPATH.  If this
proves useful, we can supply a more convenient user interface
to supply the paths.  For now, this remains somewhat experimental.

Make it easier for users to make use of the backup _tkinter linked
with the third-party Tcl and Tk frameworks in /Library/Frameworks.
The two tkinter variants are now installed in separate directories
under a new lib-tkinter.  This allows per-user selection by
manipulating sys.path, directly or with PYTHONPATH.  If this
proves useful, we can supply a more convenient user interface
to supply the paths.  For now, this remains somewhat experimental.

- added test cases to ensure docstrings are reasonable
- also updates various comments in contextlib for accuracy
- identifed #19404 as an issue making it difficult to provide
  good help output on generator based context manager instances