examples/pylab_examples/contour_demo.py fails

[mdboom]

git bisect suggests it's this revision after which it was broken:

413581c

Assigning @efiring because it might be obvious to him, but if not, I'm happy to take a further look.

Traceback (most recent call last):
  File "contour_demo.py", line 101, in <module>
    plt.flag()
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/pyplot.py", line 3344, in flag
    im.set_cmap(cm.flag)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/cm.py", line 285, in set_cmap
    self.changed()
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/contour.py", line 984, in changed
    cm.ScalarMappable.changed(self)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/cm.py", line 336, in changed
    self.callbacksSM.process('changed', self)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/cbook.py", line 312, in process
    proxy(*args, **kwargs)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/cbook.py", line 239, in __call__
    return mtd(*args, **kwargs)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/colorbar.py", line 849, in on_mappable_changed
    self.update_normal(mappable)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/colorbar.py", line 884, in update_normal
    self.add_lines(CS)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/colorbar.py", line 872, in add_lines
    erase=erase)
  File "/home/mdboom/python/lib/python2.7/site-packages/matplotlib/colorbar.py", line 498, in add_lines
    for lc in self.lines.pop():
TypeError: 'LineCollection' object is not iterable

[efiring]

Strange. I was sure I tested that whole pull request with this demo--but apparently not. I'll have to sort it out. I think I see roughly where the problem is coming from--a change from a LineCollection to a list of LineCollections, which is not being taken into account everywhere.

[efiring]

I see it--a silly bug. Fix will be available shortly.