pylab refactored; new pyplot; please test

The pylab namespace has gradually gotten messier and messier, with all sorts of things dumped into it. A number of people have asked for a smaller module that would contain only the state-machine plotting part of pylab--that is, the figure, show, plot, contour, etc. sorts of functions. The name "pyplot" was suggested. I have made a first cut at this in svn, and I hope interested people will take a look and try it out. Here are the changes:

1) pylab is still present as a namespace aggregator, importing things from numpy and pyplot. So as to avoid breaking existing code that uses it, I have kept the numpy.oldnumeric imports rather than importing from numpy itself, but it is done explicitly rather than via numerix. We will want to make a transition away from oldnumeric, but I did not want to force that immediately. The present pylab should work like the old one, except that I removed a few redundant imports. It is possible that some user code was using them and will therefore fail, but I expect such cases, if any, to be rare and easy to fix.

2) matplotlib.pyplot has all the basic function-based plotting and global things like rc and rcParams. If you want a fully modern version of pylab in interactive mode, then instead of

from pylab import *

you would do

from numpy import *
from matplotlib.pyplot import *

The latter may be what pylab itself evolves into.

Note that although gets installed as a top-level module, pyplot does not; you have to qualify it with "matplotlib".

pyplot imports a number of classes from matplotlib in addition to the basic functions. If there is a consensus that this should not be done--that pyplot should be a smaller and cleaner namespace--it would be easy to take out those imports.

I have not written a docstring for yet. I will do that once it has been checked out and the design has settled down.