Express autosave interval in minutes

Hey,

I modified my copy of the autosave module to express the interval in minutes

I changed the Drupal.autosaveAttach function in autosave.js to assign period like so:
period = Drupal.settings.autosave['period']*6000;

and changed the text in the module file to refer to minutes rather than milliseconds. This improves the usability (at least for me) because I am unlikely to _ever_ have an autosave that is less than one minute in granularity, and it means i don't have to pull out the calculator when i want to change from 2 minutes to 3 minutes.

Another suggestion would be to pop up a small animated graphic (or even greyed out text) saying "Auto saving..." when it puts the request in, since sometimes you are talking to a webserver that is far off, and it is nice to know that it has attempted to autosave.

Nice job though, the functionality is really cool, and it is a must have feature for drupal ;)