switching output formats within a function

* when saving from the GTK window into a .ps file, the

    > lines are not clipped by the edge of the plot area: see
    > the top left plot in the attached code

I've made a number of changes to matplotlib to improve the PS
functionality -- those of you who are interested should take this
version for a test drive and let me know of any problems so I can fix
them for the next release.

  http://nitace.bsd.uchicago.edu:8080/files/share/matplotlib-0.42g.tar.gz

Note WX is not working (but will be soon) with this snapshot so wx
users please do not download.

Added:

  * I think I've fixed all the backend switching problems, you can now
    output PS from the GTK backend by adding the PS extension. This
    will be available in WX soon. Let me know if you find any
    lingering bugs.

* EPS (at long last!). Just use an 'eps' extension and the bounding
   box will be added to the PS output.

    > * xaxis and yaxis labels often land on top of adjacent
    > subplot titles and plot areas in savefig('blah.ps')
    > output (I've had trouble with this in the -dPS output
    > too)

Yep, axes don't communicate with one another for text layout. A few
things which you can do to help

1) Turn off redundant x labels. If 2 subplots use the same x axis,
    turn off the tick labels in all but the lower one with

    set(gca(), 'xticklabels', [])

2) Make the tick labels and titles smaller

    t = get(gca(), 'xticklabels')
    set(t, 'fontsize', 8)

    t = title('my title')
    set(t, 'fontsize', 10)

3) control the placement of the title manually

    t = title('my title')
    t.set_y(0.95)

    1.0 is the top of the y axis. 1.02 is the default. Numbers less
    than 1 will be below the y axis. Eg, to make the title top
    aligned and below the top of the y axis, do

    t = title('my title', verticalalignment='top')
    t.set_y(0.99)

I'm open to suggestions for changing the defaults (eg making the
default fonts smaller) if people are having these kinds of problems
regularly.

JDH