Add option to append "/all" suffix for taxonomy aliases

This is a simple patch that adds the option to append the /all suffix to taxonomy aliases.
So instead of:
taxonomy/term/1 => topics/computers
you get
taxonomy/term/1/all => topics/computers

and if set the feed to all/feed
you will also get
taxonomy/term/1/all/feed => topics/computers/feed

The way pathauto generates forms and options is not very modular as far as I could tell. Meaning that all modules are expected to have the same options. I simply added the form item to form['taxonomy'] and append the /all suffux based on that setting. I was not able to over-ride the default behavior the way I would have liked because the alias checks removed the prefix.

I am somewhat familiar with tokens and originally tried adding it that way but couldn't get it to work for the same reasons.
Having a global API is good as long as it allows exceptions.

If there is a better way to do this, please make it better.
This is a simple hack that worked for my needs and I am hoping it might benefit someone else as well.