matplotlib-0.50 alpha release

I've spent the last couple of days refactoring the matplotlib
backends, fixing bugs and adding some functionality. Here's a
synopsis of what's new. I encourage everyone to try it out so
complaints and bugs can be handled before the major release.

** Note there are some API changes so please read about this below **

** Note, GD users, GD rendering is significantly improved in my
   opinion. However, some of new functionality requires a recent
   version of gd and a patch of the latest gdmodule, see below **

What's new in matplotlib 0.50e

  GD supports clipping and antialiased line drawing. The line object
  has a new 'antialiased' property, that if true, the backend will
  render the line antialiased if supported. **You will need to
  upgrade to gd-2.0.15 or later and gdmodule-0.51. You will also need
  to replace _gdmodule.c with the code as described at

wild and wonderful bar charts

  You can provide an optional argument 'bottom' to the bar command to
  determine where the bottom of each bar is, default 0 for all. This
  enables stacked bar plots and candelstick plots --
  examples/ Thanks to David Moore and John Gill for
  suggestions and code.

Bugfixes (by backend)

    * All : the yticks on the right hand side were placed incorrectly,
      now fixed

    * All : ticklabels now make a more intelligent choice about how
      many significant digits to display

    * GD : An int truncation bug was causing the dotted lines to

    * GD and GTK : Fixed line width to scale with DPI

    * GD : Fixed small text layout bug

    * GD : Fixed the constant for GD which maps pixels per inch - this
      should give better agreement with other backends witht he
      relative sizes of objects

    * GTK : Dash spacing was not properly scaling with DPI

Figure backend refactored

  The figure functionality was split into a backend independent
  component Figure and a backend dependent component
  FigureCanvasBase. This completes the transition to a totally
  abstract figure interface and improves the ability the switch
  backends. See the file that comes with the
  src distro for information on migrating applications to the new API.
  All the backend specific examples have been updated to the new API.

John Hunter