axes_grid1: ImageGrid respect the aspect ratio of axes. This addresses #955
Add default kwarg to datestr2num to fix #2481
Fix Tk keyboard modifier masks on Windows
Allow empty datasets to be passed to hist, as long as at least one dataset has data
Fixed another location where empty datasets in hist caused exceptions
Add test for histogram with empty dataset
Merge pull request #2696 from cgohlke/patch-3

Fix Tk keyboard modifier masks on Windows
Merge pull request #2481 from mdboom/datestr2num-fix

datestr2num of year and month fails on 29th, 30th, and 31st of month
Merge pull request #2248 from leejjoon/axes_grid1_axes_aspect_fix2

axes_grid1: ImageGrid respect the aspect ratio of axes.
Add cleanup to test
Package initialization made possible when executed in environments whithout access to the home directory.

Functions _get_xdg_config_dir(), _get_xdg_cache_dir(), _get_config_or_cache_dir() allow now the use of the environment variables XDG_CONFIG_HOME resp. XDG_CACHE_HOME without requiring access to the home directory (f.ex. in batch jobs on clusters).

Before, the definitions of the environment variables would not have been used when the home directory was not accessible. Nevertheless, the standard does not bind the variable definitions to the existence of home directories (only the default values are defined with respect to them).
Merge pull request #2719 from michs/xdg_home-config

Package initialization made possible when executed in environments with...
Merge pull request #2551 from neggert/hist_emptydata

Fix behavior of hist function when passed empty dataset
Merge remote-tracking branch 'upstream/v1.3.x'

Conflicts:
	lib/matplotlib/axes/_axes.py
	lib/matplotlib/dates.py
	lib/mpl_toolkits/axes_grid1/axes_grid.py