The plot function in ConditionalFreqDist was throwing an ImportError
because it was trying to import 'plt' from matplotlib which does not
exist. Additionally the methods called were still the methods of
they pylab submodule and I updated those calls to those of the pyplot
submodule. Additionally the if v in self key check would not pass
with valid input so I removed it and the function now plots correctly.

Was calling ax.set_xticks which was not displaying the correct labels
so I changed it to use the pyplot.xticks method which works correctly
with the input that was being given to set_xticks.