text rotation_mode

Hi,

I just committed a simple patch that introduces a "rotation_mode"
property for Text artist.
By default, mpl rotates the text first and then align it. The patch
let it (optionally) align then rotate (see
examples/pylab_examples/demo_text_rotation_mode.py).
I have chosen "anchor" as the mode name for the latter, but I'm not
sure if this name makes any sense. Any suggestion will be very
appreciated.

-JJ