BUG : fix list comprehensions over class members

Due to scoping fixes in py3k, list comprehensions over class level
attributes during class definition does not work (see
http://stackoverflow.com/questions/13905741/accessing-class-variables-from-a-list-comprehension-in-the-class-definition).

Superficially Fixes #3436. There seem to be other issues
BUG : fix glaring syntax error
BUG : fix encoding of png data

When formatting the png data to send over the wire need to decode the
byte string to ascii.  If this is not done the literal string sent
to the browser is:
   "data:image/png;base64,b'iVBOR...'"
instead of
   "data:image/png;base64,iVBOR..."

The extra b' makes the string no longer a valid png which is why
we were getting white boxes
Allow running from non-ascii directory on Windows
BUG: Take the absolute difference between times when determining the correct tick interval
BUG : fix eps corruption when using clipping

_get_clip_path was returning '<built-in function id>' instead
of the ps-function name like it should have been.  This was introduced
in 9b9c0c6fbdd53ec42e2a1edecc9c6895b6f7a3ef in PR #2927.

Closes #3523
Merge pull request #3526 from tacaswell/fix_eps_clip_paths

BUG : fix eps corruption when using clipping
Only insert links to pdfs if we are actually generating these. This should
silence most warnings in the html only small build on travis
Merge pull request #3487 from mdboom/use-getcwdu

BUG : use getcwdu to deal with unicode in user home-path in python 2
Merge pull request #3530 from jenshnielsen/travis_docs

BUG : Only insert links to pdfs if we are actually generating these.
Merge pull request #3510 from blink1073/fix-setupext

BLD : improve setupext.py on windows
BUG/DOC : Correct default value listed in docstring

Changed to be True to match the code

closes #3455
Merge pull request #3369 from e-q/legendFrameAlpha

BUG : Added legend.framealpha to rcParams, as mentioned in axes.legend docstring
Merge pull request #3535 from tacaswell/boxplot_doc

BUG/DOC : Correct default value listed in docstring
BUG : fixes whis over-writing in boxplot_stats

Restore the value of `whis` to the input value at the top of each pass
through the for-loop.

@weathergod hit the nail on the head.

closes #3468
Merge pull request #3534 from tacaswell/bxp_whis_fix

BUG : fixes whis over-writing in boxplot_stats
Merge pull request #3464 from tacaswell/nbagg_py3k

BUG : nbagg py3k compatibility
DEP : update six minimum version

 turns out we really need version 1.4 or better

fixes #3538
TST: Added test for inverted limit with autodatelocator
STY/TST: pep8 fixes for test_dates