Sets _NET_NUMBER_OF_DESKTOPS and _NET_CURRENT_DESKTOP on root to appropriate values. Note that 'appropriate' for these values don't make sense as xprop -root output, since dwm uses them at bitwise but xprop displays them in base ten. In other words, if you have 4 desktops, _NET_NUMBER_OF_DESKTOPS is actualy 0b1111 but xprop displays this as 15. I'm ok with this, because the end-user (program, script, w/e) can always parse this appropriately. The same goes for _NET_CURRENT_DESKTOP: if you have desktops 1 and 3 selected, the value is 0b1010, but xprop shows this as 10. This isn't a problem.

I should note that in this case, _NET_NUMBER_OF_DESKTOPS does not exactly conform to EWMH specifications: in reality, there are many more 'desktops' than 15 (in the above example), as any combination of 1, 2, 3 or 4 of the availables tags can be considered one desktop. _CURRENT_DESKTOP will, however, always be less that _NET_NUMBER_OF_DESKTOPS, so I'm happy with that.

I wrote this patch mainly for myself, as I have a script for tabbed that uses it (I will upload this later). I am open to feedback/contstructive criticism. Email is at the bottom.