pil_plugin can import and export from memory

- added capability to import and export to PIL Image
  objects, not just files - allows for converting
  to and from PIL image objects without writing
  to disk
- no unit test yet
added tests for roundtrip export and import

- and corrected error in imexport - wasn't using imsave code
  correctly
- split imsave into imsave and imexport functions to reuse
  imsave code
added a space character to trigger travis build
fixed bad indent
improved name of pil import/export functions

- to make it clear what the functions actually do:
  ndarray_to_pil() and pil_to_ndarray()
- as per code review feedback
- updated tests to use the new function names

- incoming change to pil_plugin assumed PIL Image
  objects will always be from files; this is
  not always true anymore. Now pil_plugin
  checks to see if the Image came from a file
  before trying to close its associated file.
First working copy
pep8 changes
Cleaned up rag.py
cleaned up _ncut.py
Docstrings
Docstring of graph_cut.py
rectified threshold mistake
docstrings to _ncut.py
docstring to _ncut_cy.pys
Comments to graph_cut.py
Added example for ncut
Updated bento file
used standard eignen solver
doc string correction
Remove unused except caluses