[dev] dwm rules do not check window's first class

[James Campos]

In dwm's config.h, I added a rule to place windows of a certain class to a
certain tag. However, windows apparently have two classes, and this rule
only works if it specifies the second class. I'd like to request that dwm
check both classes, since the program I was writing the rule for, st, only
changes the first class with the -c switch.