Add formatting to the DateY X axis label
Allow formatting other than the default for the X axis on the DateY plots.
This is done by setting
datey.x_label_format = "%Y-%m-%d"

The formatting is done by the strftime function, so any valid format will work.
See: http://docs.python.org/2/library/time.html#time.strftime
Merge remote-tracking branch 'philt2001/master'