Rewrite and greatly simplify qt_compat.py.
Conflicts:
        INSTALL.rst
          - kept changes away from App specific wording
          - kept min pyqt4 version bump
	doc/sphinxext/mock_gui_toolkits.py
          - only removed setting up the Qt mocks
	lib/matplotlib/backends/qt_compat.py
          - kept backported version, conflict was in block of
            constants at top (all of the contestants are still
            defined in the module)

…rm-limits

FIX: image respect norm limits w/ None
Conflicts:
	lib/matplotlib/image.py
          - keep changes backported from master.  Looks like conflict
            was due to some white-space clean up done on master.

Add note about hist2d resetting axis limits

Conflicts:
	lib/matplotlib/axes/_axes.py
          - kept master branch version of docstrings

Propagate marker antialias setting to GraphicsContext.

…-alpha

FIX: When drawing markers, don't set the GraphicsContext alpha.
Conflicts:
	lib/matplotlib/lines.py
          - keep aliases (which are implemented automatically on
            master) explicitly in code

Use dummy_threading if threading not available
Conflicts:
	lib/matplotlib/backends/backend_agg.py
          - conflicts due to removing __future__ / six on master

This also backported parts of other PRs making changes to the docs.

Replace :ref:`sphx_glr_...` by :doc:`/...`.
Conflicts:
	examples/color/color_cycler.py
          - deleted, not present on 2.2.x
	examples/axes_grid1/simple_anchored_artists.py
	examples/images_contours_and_fields/contour_image.py
	examples/images_contours_and_fields/quiver_demo.py
	examples/images_contours_and_fields/quiver_simple_demo.py
	examples/misc/anchored_artists.py
          - keep master version

…strings-with-escape

Use raw string literals for docstrings with escapes

Conflicts:
	lib/matplotlib/artist.py
          - reject py2 incompatible changes
	lib/matplotlib/axes/_axes.py
         - also backports some documentation changes

FIX: Properly position markers in step plots.

Conflicts:
	lib/matplotlib/tests/test_lines.py
          - conflict due to adding imports around (removed on master)
            __future__ and six

DOC: Use plt.subplots()

Conflicts:
	lib/matplotlib/tests/test_backends_interactive.py
          - only backported the minimal change
	tutorials/advanced/transforms_tutorial.py
          - only backported the minimal change
	tutorials/text/pgf.py
          - only backported the minimal change

DOC: warn if user is using constrained layout and uses subplots_adjust

Conflicts:
	lib/matplotlib/figure.py
           - signature on master has changed to explicit kwargs,
             conflict due to that change.

This context manager was added to master in
690b213 via matplotlib#10314.  We do not want
to backport that entire commit, however the backport of matplotlib#11407
requires this context manger.

It is private and self contained to low-risk to backport