KILL [CONNECTION | QUERY] support, part1

Preparation for adding KILL syntax support.
Session id changed to uint32 everywhere. Added atomic op.
Session id can be acquired before session_alloc().
Added session_alloc_with_id(), which is given a session id number.
Worker object has a session_id->SESSION* mapping, not used yet.

server/modules/routing/debugcli/debugcmd.c

@@ -1724,7 +1724,7 @@ convert_arg(char *arg, int arg_type)
         break;
 
     case ARG_TYPE_SESSION:
-        rval = (unsigned long)session_get_by_id(strtol(arg, NULL, 0));
+        rval = (unsigned long)session_get_by_id(strtoul(arg, NULL, 0));
         break;
 
     case ARG_TYPE_MONITOR: