Fix compilation on Solaris
Merge branch 'v1.3.x'

* v1.3.x:
  Document API change in hist
patch to fix issue #2473.

The change to the agg propagate to how `imsave` works so one test had
to be changed to account for the fact that pixels with alpha=0 are now
set to (1, 1, 1, 0) instead of (0, 0, 0, 0).
added class variable `_fill_color` to RendererAgg to hold the
color to use in `clear` calls to the render_base.

Changed all uses of `clear((...))` -> `clear(_fil_color)`.
changes to c++ because gcc 4.8 seems to allow things the compiler
on travis will not.
Fix #2472: Draw the spines on top of twin axes
fixed an enconding bug when checking for gs version
Updated the docs of pyplot.gca.
Merge pull request #2502 from pelson/gca_doc

Updated the docs of pyplot.gca.
minor docstring fix in dates.py
tiny correction of matplotlibrc.template

remove quotes around text.hinting default value (i.e. auto)
pep8
- pep8
 - removed mutable default values
 - foo == None -> foo is None
Merge pull request #2472 from mdboom/twin-spines-on-top

Plots using twinx draw on top of figure frame
Merge pull request #2479 from tacaswell/rastized_background

Set default agg canvas background color to ```(1, 1, 1, 0)```, rather than ```(0, 0, 0, 0)```.
Update version to 1.3.1
add more spectrum functions and add new spectrum types to specgram in mlab.py, and clean up window and detrend functions in mlab.py
add mlab tests for new spectrum types, window and detrend functions, and greatly expand existing tests
add CleanupTestCase, a unittest.TestCase with cleanup
refactor mlab spectrum, window, and detrend functions to improve modularity, testability, and performance