Add a fix for Python bug #20108

[jdemeyer]

ipywidgets uses inspect.getcallargs which has a subtle bug in case the inspected function has a func keyword argument: http://bugs.python.org/issue20108

This is fixed in Python 3.3 and later. We can easily backport the fix to Python 2.7.

While I'm at it, I also removed sdist.patch (which was about .hg directories and is clearly no longer relevant) and renamed some patches with the Python issue number.

Note to the release manager: ideally, this would be merged together with #21441 since both tickets trigger recompilation of all Python packages.

Upstream: Fixed upstream, in a later stable release.

CC: @EmmanuelCharpentier

Component: packages: standard

Author: Jeroen Demeyer

Branch/Commit: cf0621d

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/21552

[jdemeyer]

Branch: u/jdemeyer/add_a_fix_for_python_bug__20108

[jdemeyer]

New commits:

cf0621d

Fix Python bug #20108: getcallargs() with func keyword

[jdemeyer]

Commit: cf0621d

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:5

Good for upstream, so good for Sage.

[vbraun]

Changed branch from u/jdemeyer/add_a_fix_for_python_bug__20108 to cf0621d