Issue 2690: Add support for slicing and negative indices to range objects (includes precalculation and storage of the range length).

Refer to the tracker issue for the language moratorium implications of this change

* A -b option to start an enhanced browsing session.
* Allow -b and -p options to be used together.
* Specifying port 0 will pick an arbitrary unused socket port.
* A new browse() function to start the new server and browser.
* Show Python version information in the header.
* A *Get* field which takes the same input as the help() function.
* A *Search* field which replaces the Tkinter search box.
* Links to *Module Index*, *Topics*, and *Keywords*.
* Improved source file viewing.
* An HTMLDoc.filelink() method.
* The -g option and the gui() and serve() functions are deprecated.

Partially revert r78719 - it removed a check that is still needed in some cases (i.e. this will allow Michael to add the test.__main__ support that broke the buildbots previously)

The motivation for adding this option is that the the functionality it
provides used to be provided by sgmllib in Python2, and was used by,
for example, BeautifulSoup.  Without this option, the Python3 version
of BeautifulSoup and the many programs that use it are crippled.

The original patch was by 'kxroberto'.  I modified it heavily but kept his
heuristics and test.  I also added additional heuristics to fix #975556,
#1046092, and part of #6191.  This patch should be completely backward
compatible:  the behavior with the default strict=True is unchanged.

Added a few common Popen uses to the tests like we've done for a few other
instances of adding context managers. Eventually the entire test suite
could be converted to use the context manager format.

Simplify the signature for itertools.accumulate() to match numpy.  Handle one item iterable the same way as min()/max().

Patch by Adrian von Bidder.

In order to create symlinks on Windows, SeCreateSymbolicLinkPrivilege
is an account privilege that is required to be held by the user. Not only
must the privilege be enabled for the account, the activated privileges for
the currently running application must be adjusted to enable the requested
privilege.

Rather than exposing an additional function to be called prior to the user's
first os.symlink call, we handle the AdjustTokenPrivileges Windows API call
internally and only expose os.symlink when the privilege escalation was
successful.

Due to the change of only exposing os.symlink when it's available, we can
go back to the original test skipping methods of checking via `hasattr`.

#7475: add (un)transform method to bytes/bytearray and str, add back codecs that can be used with them from Python 2.

#10597: fix Py_SetPythonHome docs by pointing to where the meaning of PYTHONHOME is already documented.