another bug in axis limits

it worked in 0.5.2

    > What is the problem?

I implemented new tick locator in 0.53 which should provide nicer
default tick locations as well as better user customization. I failed
to test for the equal data limits case, which several people have
already reported. This is fixed in CVS.

Early next week, probably Monday, I will accumulate all the reported
bugs and fixes into a 0.53.1 release, so please continue to let me
know as you find them.

Note if you actually want to see the result of your plot, you'll need
to add a marker

  from matplotlib.matlab import *
  plot ([1], 'o')

since otherwise you have a zero length line.