setting grid density

This one is 1h per minor grid and tick, 6h per majors.

Hi Phillipe,

I just wanted to let you know that I've finished adding the major and
minor tick support for the next release of matplotlib. There is
additional support for plotting dates and formatting dates with major
and minor ticks. There are specialized tick locators for marking
ticks by minute, hour, day, weekday, month, year, every 4 hours, every
3 months, and so on. There is a new command plot_date function and a
series of date converters to let you plot dates with, for example,
epochs, python datetimes or mx.Datetimes. You can work with custom
date instances by supplying a custom converter. You can format the
date ticks with strftime strings of your choice.

The major and minor tick support is generic and fully customizable and
should be useful for many other applications.

Look for the release next week.