Fix bugs related to bottom kwarg in step histograms

Conflicts:

	lib/matplotlib/axes.py
	lib/matplotlib/tests/baseline_images/test_axes/hist_step.png
Added methods to control theta position of r-ticklabels on polar plots
Merge pull request #2550 from joferkington/fix-wx-singleshot-timer

Using a single-shot timer with the Wx backend raises an AttributeError
pep8 for backend_pdf.py
remove backend_pdf from pep8 test exclude list
minor code standard changes
minor code formatting
more informative exceptions for empty/not-existing images in
compare_images()
AffineBase.__eq__ should not raise an exception when the other does not have "is_affine" attribute.
Merge pull request #2581 from leejjoon/affine_base_eq

AffineBase.__eq__ should not raise an exception when the other does not ...
Merge pull request #2584 from magnunor/fix_legend_typo

Fix typo in legend documentation
Merge pull request #2591 from dopplershift/fix-infinite-recursion

Fix infinite recursion in units with ndarray subclasses.
partial coloring of text: unicorn poop example
finish adding rainbow_text example, closes #697
adjust text size to fit in html docs
fixed naming and spacing issue, just for @pelson
ax is now an optional argument to rainbow_text

I hope @pelson and @tacaswell realize that this is just an example
gallery file when they were doing their code review
Add easy style sheet selection.
Add rc_params_in_file to return partially-filled RcParams

This allows style sheets to update the current settings instead of overwriting them.
Rename style files to `*.style`