New template tag for preventing graphs running out of table

Hi.

I've found that, when going up to more than 100%, the graphs goes out of the data table.

In order to correct this and keep the graph bar inside the table, I slightly modified the Django ``widthratio`` template tag, which you are using to render the percentages and draw the graphs. This template tag can be found in ``django.template.defaulttags``.

So, what I exactly did is to copy this tag functionality, but limit the output number to a maximum of 100%, so when you have data which passes it, it will stop at 100% instead of, for example, drawing a 800% bar. You can use this ``safewidthratio`` tag wherever in the HTML you are going to render a graph bar, keeping the ``widthratio`` tag in places where you render the exact number as a string, so you can get the table representing good data, but with the graphs inside the table.

I attach two images, before and after my code, so you can see more exactly what I mean.

Before my additions:
![screen shot 2013-06-21 at 3 30 42 pm](https://f.cloud.github.com/assets/2226098/691944/b030d758-dbde-11e2-948a-55daaa6692b0.png)

After my additions:
![screen shot 2013-06-23 at 10 15 18 am](https://f.cloud.github.com/assets/2226098/691945/be46ea76-dbde-11e2-9a09-826c512a83e2.png)

Hope you find this useful.

Cheers.