fix Unix build with DEF_PAGER defined

Eliminate a couple of compile warnings produced when DEF_PAGER is
defined:  unixmain.c: g.catmore=DEF_PAGER; wintty.c: fd=open(...).

Override its use when DLB is also defined since an external pager
could access 'license' but not 'history', 'opthelp', &c when those
are in the dlb container file.

In the commented out value for DEF_PAGER, show a viable value for
the default configuration these days.

sys/unix/unixmain.c

@@ -220,7 +220,8 @@ main(int argc, char *argv[])
 #endif
 
 #ifdef DEF_PAGER
-    if (!(g.catmore = nh_getenv("HACKPAGER"))
+    if (!(g.catmore = nh_getenv("NETHACKPAGER"))
+        && !(g.catmore = nh_getenv("HACKPAGER"))
         && !(g.catmore = nh_getenv("PAGER")))
         g.catmore = DEF_PAGER;
 #endif