multiple plots fail in TkAgg interactive

I can't seem to get multiple plots to draw on the same

    > figure under TkAgg. In the below example, the cos()
    > doesn't show up, and the tan produces an error. This
    > seems to be repeatable for arbitrary cases of trying to
    > plot 2 or 3 lines together on the one plot.

Found and fixed. This crept into the functions that process plot
arguments when I added matplotlibrc support there. In, search
for def _plot_1_arg and replace the first part of it with

    def _plot_1_arg(self, y, **kwargs):
        if self.count==0:
            color = self.firstColor
            color = self.colors[int(self.count % self.Ncolors)]
                      ^^^ this is the critical part

    > Cheers and thanks for matplotlib, Matthew.

Thanks for the bug report!