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
ENH: optimized label2rgb()
Deprecate default mode 'bf' in random_walker
Add change in random_walker default mode to TODO
Update SLIC in example to most recent interface

SLIC has been updated a few times since this example was created,
adding support for grayscale images (so converting to RGB is no longer
necessary) and changing the keyword "ratio" to "compactness". This
commit brings the example up to date.
fixed error in label2rgb() when label is a binary array
Merge pull request #762 from jni/update-slic-example

Update SLIC in example to most recent interface