Fix accidental merge
pep8 fixes
made example clearer
 - use OO interface to set tick labels rather than pyplot
 - explicitly set ax2.ylim, rather than relying on auto-scale magic
Merge pull request #2325 from matthew-brett/deal-with-broken-qt4

BF: guard against broken PyQt import
Merge pull request #2316 from vbr/patch-6

Replace the obsolete wx.PySimpleApp