tick locators and formatters

I overhauled the tick locator and formating in matplotlib CVS. This
provides a lot of nice features, like easily setting major and minor
ticks on multiples of some number, auto locators that pick good ranges
and tick locations dynamically during navigation, a bevy of datetime
tick locators and formatters. If major and minor tick locators are
present, only the major tick locator is used for axis autoranging.

For tick formatting, you can use autoformatting (the default), fixed
tick labels, sprintf format strings, user defined functions, strftime
date format strings or custom classes. This is described in detail in
the matplotlib.dates and matplotlib.ticker module documentation in

Perry had mentioned that his group was very interested in some custom
major and minor tick locators and formatters of interest to
astronomers. So if you want to start adding these (or anyone else who
wants to add some useful ones for their application domain), please
check them into CVS or send them to the list.

The new examples major_minor_demo*.py and date_demo*.py show how to
use the new classes.