Don't return an error if the node#/node.cnf file can't be opened for all uses of load_cfg() except from the terminal server. This fixes #214 for Tracker1

gtkmonitor.c:156:79: warning: iteration 9 invokes undefined behavior [-Waggressive-loop-optimizations]
   sprintf(str,"%-2d  SL: %-2d  F1: %s",i,cfg.val_level[i],ltoaf(cfg.val_flags1[i],flags));
                                                                 ~~~~~~~~~~~~~~^~~
gtkmonitor.c:151:2: note: within this loop
  for(i=1; i<=10; i++) {
  ^~~

not set (or blank), use the default ("/sbbs/ctrl") and print a warning to
stderr. This resolves a FAQ for sysops that struggle with setting the SBBSCTRL
env var, but do have sbbs install in /sbbs or a symlink from /sbbs to where
sbbs is actually installed.

Note: this function is different than the one previously defined in getctrl.c
but never used. If/when we ever really need to support PREFIX, then perhaps
we'll use that one (which copies a string to a buffer).

targets.mk:8: *** missing separator (did you mean TAB instead of 8 spaces?).  Stop.

about undefined targets.

GtkBuilder era.

Thanks rfrederick!