matplotlib has remove hold() method

[pkienzle]

sasview 4.x, recent versions of matplotlib. Don't know if ESS gui uses hold().

With a recent matplotlib package from anaconda I get the following error:

Traceback (most recent call last):
  File "/Users/pkienzle/Source/sasview/src/sas/sasgui/guiframe/local_perspectives/plotting/plotting.py", line 326, in _on_plot_event
    new_panel = self.create_1d_panel(data, group_id)
  File "/Users/pkienzle/Source/sasview/src/sas/sasgui/guiframe/local_perspectives/plotting/plotting.py", line 197, in create_1d_panel
    ytransform=ytransform, style=wx.RAISED_BORDER)
  File "/Users/pkienzle/Source/sasview/src/sas/sasgui/guiframe/local_perspectives/plotting/Plotter1D.py", line 92, in __init__
    self.graph.render(self)
  File "/Users/pkienzle/Source/sasview/src/sas/sasgui/plottools/plottables.py", line 314, in render
    plot.clear()
  File "/Users/pkienzle/Source/sasview/src/sas/sasgui/plottools/PlotPanel.py", line 1237, in clear
    self.subplot.hold(True)
AttributeError: 'AxesSubplot' object has no attribute 'hold'

They did warn us it was going away eventually:

​https://matplotlib.org/api/_as_gen/matplotlib.axes.Axes.hold.html

[Paul Kienzle <pkienzle@…]

In 9305b463663a5933a89dce367a0dc29fc9d712e8/sasview:

matplotlib hold now permanently set to True. Refs #1266.