Move widget.{get,set}_active to AxisWidget.

The method was previously defined only for RectangleSelectors (#3375).

Also, an redundant line was removed (RectangleSelectors are already set
active on __init__ by the superclass).
Update background on widget.set_active(True).

Because selectors must update their background on set_active(True),
widget.active was made a property for backwards compatibility.
Updated whats_new.rst.

Because _Selector is a private class there are no references to the
actual getter and setter in the rst file.
Minor fixes according to Github discussion.
_SelectorWidget overrides the active property.

... so it should dynamically retrieve the set_active method.
Better repr for Bboxes.
Actually eval'able __repr__ for Bboxes.
__str__ & __format__ for Bboxes, and tests.
Merge pull request #3469 from mfitzp

Fixed pep8 and merged to master locally
BUG : restore back-compatibility of regisiter_backend

revert back-incompatible change from
8159c817bb41dc0c3d86aa909318eb3e55a64d8f

closes #3439
Merge pull request #3467 from cimarronm/mlab_stride_bugfix

BUG : Bugfix in mlab for strided views of np.arrays
Merge pull request #2900 from bytbox/master

TST : Remove no-longer-necessary KnownFail for python 3.2.

no longer needed, because we are no longer testing 3.2
Merge pull request #3478 from tacaswell/regisiter_backend_compat_fix

BUG : restore back-compatibility of regisiter_backend
Merge pull request #3474 from fariza/change-cursor-inmediately

ENH : call set cursor on zoom/pan toggle
Merge pull request #3419 from anntzer/bbox-repr

ENH : Better repr for Bboxes.
Merge pull request #3376 from anntzer/widget-active-setter-getter

ENH : Move widget.{get,set}_active to AxisWidget.
BUG: Missing return on xytext property
Merge pull request #3501 from cimarronm/text_xytext_bugfix

BUG : Bugfix for text.xytext property
Merge pull request #3501 from cimarronm/text_xytext_bugfix

BUG : Bugfix for text.xytext property
fix winbuild link