[dwm] nmaster patch

This is a very simple patch which doesn't add any line of code (except
one unnecesary line in config.h to define a new tile symbol). It
allows having an nmaster == 0, so all your windows are in the stack
having all the width of the screen and the same height. I don't really
use widelayout or all my clients in master area, but just noticed this
way we have the same behaviour and somebody could find it interesting.
It would be necesary to add one or two lines of code in incnmaster to
being able to set this mode with just one keystroke (i think).
Id like to see some comments.

Note: add to your config.h
#define NOMSYMBOL "[==]"
or whatever you like, else you will have a compilation error. If you
don't want a new symbol and prefer "[0]=" keep your actual
updatemodetext()

Regards,

--
- yiyus || JGL .