Improving docstring + style/convention edits
Added some warnings for transparency.
PEP8 compliance!
One line.
Changed variable names so they actually make sense (followed Tony's
suggestion).
Hide experimental GSoC functions for 0.9 release
Temporarily remove censure keypoints example
Update PR plotter.
Correctly plot cumulative sum.
Only raise umfpack warning if cg mode is used
Monkey-patch UmfpackContext __del__

By putting the failing statement in a try: except: clause, the
exception is caught and the error message is silenced.

See
https://groups.google.com/d/msg/scikit-image/FrM5IGP6wh4/1hp-FtVZmfcJ
and
http://stackoverflow.com/questions/13977970/ignore-exceptions-printed-to-stderr-in-del/13977992?noredirect=1#comment28386412_13977992
Tiny formatting edits
Remove unused imports in random_walker source
Add comment and links explaining Umfpack import
Deprecate default mode 'bf' in random_walker
Add change in random_walker default mode to TODO
BUG: basestring not defined on PY3
TST: use BytesIO to save images into file-like object

StringIO does not work on Python 3
Add support for consistent color labels for sparse labels.
BUG: Fix ValueError: Buffer dtype mismatch, expected 'long' but got 'long long'

on win-amd64