tools/dirtpan/dirtpan.c: new option -b to background/daemonize
tools/dirtpan/dirtpan.c: new option -b to background/daemonize

- dirtpan.c (usage): added detailed description of the arguments
- dirtpan.c (usage, main): new option -b to daemonize after initialization

cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan