Initial structure for supervisor-mode

The full process hierarchy isn't set up yet, but these changes
help prepare by doing two things:

- Add a -j option to enable supervisor-mode.  Currently, just a single
  "stem" process gets forked early on to be used as the basis for
  further forking into real cluster nodes.

- Separates the parsing of command-line options from their consumption.
  i.e. need to parse whether we're in -j supervisor-mode before
  modifying any global state since that would taint the "stem" process.
  The new intermediate structure containing the parsed options may
  also serve as a way to pass configuration info from "stem" to its
  descendent cluster node processes.

src/DebugLogger.h

@@ -29,6 +29,7 @@ enum DebugStream {
 	DBG_PKTIO,	// Packet sources and dumpers.
 	DBG_BROKER,	// Broker communication
 	DBG_SCRIPTS,	// Script initialization
+	DBG_SUPERVISOR,	// Process supervisor
 
 	NUM_DBGS // Has to be last
 };