Properly passing on horiz-/vertOn to Cursor()

Simple fix to properly pass on the horizOn and vertOn keyword
arguments to the matplotlib.widgets.Cursor constructor.
Make Axes.stem take at least one argument.

When it takes only one, the abscissae default to np.arange(len(y))
Add axes.stem call signature test
Update CHANGELOG with axes.stem change
Improve empty collection check in add_collection.
use QMainWindow.closeEvent for close events

The current code uses the QWidget.destroyed signal
to emit a close event into matplotlib. This is a very
bad idea, as it is a heavy abuse of Qt functionality.

When a main window is closed in Qt, it and its children
are deleted if the DeleteOnClose flag is set (which we
did set). This causes the QWidget.destroyed signal to be
called. Setting the DeleteOnClose flag is a very bad
idea, since objects should only be deleted by the
garbage collector. Soon after, PyQt4 will complain
that "the underlying C++ object has been deleted", since
the object is alive for python but dead for C++.

This patch changes the machinery to use the
QMainWindow.closeEvent to emit a close_event, which is
what one actually wants.
Add test for add_collection
Fix positional argument parsing
Make stem catch explicit Exception classes
Make `rc_context` available via pyplot interface
inverting an axis shouldn't affect the autoscaling setting
Renamed all instances of variables named "long" to "lon" to avoid clobbering by 2to3
Remove NO_DEPRECATED flag -- this was accidentally committed.
Added a test for #1553
make rc_context show up in pyplot's docs
Remove redundant ob_refcnt's that cause crashes when built in DEBUG mode.
fix issue #1572 caused by PR #1081
Fixed blitting in Gtk3Agg backend to redraw only area defined by bbox (#1575)
Updated custom_projection_example.py to work with v1.2 and newer\nSee <http://www.mail-archive.com/matplotlib-users@lists.sourceforge.net/msg25935.html> for a more complete discussion.
Merge pull request #1573 from pwuertz/fix_1572

fix issue #1572 caused by PR #1081