Patch adding minor ticks that autoscale


It has always bugged me that it's not easy to display minor ticks in matplotlib,
and there is no easy way to make minor ticks autoscale the same way major ticks

I just added a patch to tracker that (I hope!) fixes these two problems.

It adds a new locator class, AutoMinorLocator, that can be used to dynamically
find minor tick positions based on major tick positions. It also adds a new
function to pyplot, minorticks(), that can be used to toggle the minorticks on
and off. Adding autoscaling minor ticks reduces performance, but not excessively
(on my Intel centrino duo laptop). They should probably be off by default though.

Any comments are welcome,