scaling bug

I think I've found a bug in matplotlib 0.53. The bug can be triggered
with the following commands

from matplotlib.matlab import *
plot(arange(40), array([1]*40))

Basically, bad things happen if you try to plot a flat line. By
themselves, flat lines aren't very interesting, but they do occasionally
show up in the automated graphing batches I do. The first problem is an
easily patched bug in where matplotlib tries to take the
logarithm of the interval span of the input data. For a constant data
series, that interval span is zero, and log(0) is naturally unhappy.

Unfortunately, after fixing that problem, another problem arises. In, a divide by zero is triggered when trying to determine
display scale for much the same reason.

I've patched these bugs as best I can, but my fix isn't worth much since
the results look awful (no tick marks, data is uncentered). Its probably
best to let someone who knows what they're doing fix this for real.

Thanks a lot,
Mike Salib