FIX: Require integer array indexing for future NumPy compatibility

This PR addresses #623. Various single `/` operations were returning floats in Python 3, so the fix was to convert them to floor division `//` to harmonize behavior and dtype with Python 2.

There are also a few PEP8 and style fixes.

@juliantaylor I'd appreciate it if you re-ran the test from #623 after pulling in these revisions, in case there's something I missed. Also, these seven deprecation warnings were from `numpy/core/numeric.py` after integer arguments were passed to NumPy functions. scikit-image may not the source of them:

* test_shape.test_view_as_blocks_1D_array ... /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:341: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
* test_shape.test_view_as_blocks_2D_array ... /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:341: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
* test_shape.test_view_as_blocks_3D_array ... /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:341: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
* /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:1627: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
* /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:1630: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
* /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:1632: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
* /tmp/local/lib/python3.3/site-packages/numpy/core/numeric.py:341: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future