Avoid using deprecated get_axis_bgcolor() method with newer matplotlib

[WeatherGod]

When plotting with newer versions of matplotlib, one gets a lot of deprecation warnings:

/rd22/scratch/broot/centos6/lib/python2.7/site-packages/mpl_toolkits/basemap/__init__.py:1652: MatplotlibDeprecationWarning: The get_axis_bgcolor function was deprecated in version 2.0. Use get_facecolor instead.
  fill_color = ax.get_axis_bgcolor()
/rd22/scratch/broot/centos6/lib/python2.7/site-packages/mpl_toolkits/basemap/__init__.py:1796: MatplotlibDeprecationWarning: The get_axis_bgcolor function was deprecated in version 2.0. Use get_facecolor instead.
  axisbgc = ax.get_axis_bgcolor()
/nas/home/broot/centos6/lib/python2.7/site-packages/matplotlib-1.5.1+1669.gbfe5e3f.dirty-py2.7-linux-x86_64.egg/matplotlib/cbook.py:137: MatplotlibDeprecationWarning: The axisbg attribute was deprecated in version 2.0. Use facecolor instead.
  warnings.warn(message, mplDeprecation, stacklevel=1)

This does a version check and uses the appropriate call instead. I think I found all instances of it.

There is still the annoying numpy warning, though:

/nas/home/broot/centos6/lib/python2.7/site-packages/numpy-1.12.0.dev0+e62aa19-py2.7-linux-x86_64.egg/numpy/ma/core.py:3192: FutureWarning: Currently, slicing will try to return a view of the data, but will return a copy of the mask. In the future, it will try to return both as views. This means that using `__setitem__` will propagate values back through all masks that are present.
  FutureWarning
/nas/home/broot/centos6/lib/python2.7/site-packages/numpy-1.12.0.dev0+e62aa19-py2.7-linux-x86_64.egg/numpy/ma/core.py:3113: FutureWarning: Currently, slicing will try to return a view of the data, but will return a copy of the mask. In the future, it will try to return both as views.
  FutureWarning