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/input.h

@@ -38,8 +38,8 @@ extern int bro_argc;
 extern char** bro_argv;
 extern const char* prog;
 
-extern name_list prefixes;	// -p flag
-extern char* command_line_policy;	// -e flag
+extern std::vector<std::string> zeek_script_prefixes;	// -p flag
+extern const char* command_line_policy;	// -e flag
 extern vector<string> params;
 
 class Stmt;