Fix bugs related to bottom kwarg in step histograms

Conflicts:

	lib/matplotlib/axes.py
	lib/matplotlib/tests/baseline_images/test_axes/hist_step.png
Merge pull request #2409 from neggert/hist_bottom_fix2

Fix bugs related to bottom kwarg in step histograms
BLD Fix build failure on Python 3.4b1 for Windows Windows

As of version 3.4b1 the official CPython distribution for Windows uses Tcl/Tk 8.6.
Merge pull request #2613 from cgohlke/patch-1

BLD Fix build failure on Python 3.4b1 for Windows
Merge remote-tracking branch 'upstream/v1.3.x'

Conflicts:
	lib/matplotlib/axes/_axes.py