[dwm] mastertag patch for dwm 3.1

Hello,
I have a vague idea this has been discussed before, but since it was a simple patch, I wrote it anyway and you can do what you like with it.
My main irratation with stock dwm* is that if you have multiple tags selected then when you create a window it will be tagged with all the currently selected tags.
Personally I have a tag I'm working on primarily, but will swap other tags in and out as I work which contain specific window(s). This tag adds a mastertag variable which is used as follows:
 * initally tag 0 is the master tag.
 * new windows are tagged with mastertag only.
 * if you switch tag with view, that tag becomes the mastertag.
 * if you toggle the master tag off the lowest selected tag becomes master.
This patch won't be for everybody, but I thought someone might have a use for it.

Regards,
Archie

*Apart from java, but my ire for that is fully aimed at sun