Prevent walking into water or lava by default

Make paranoid_confirmation:swim the default, because it is far more
beginner friendly.

src/options.c

@@ -6085,7 +6085,7 @@ initoptions_init(void)
     flags.end_own = FALSE;
     flags.end_top = 3;
     flags.end_around = 2;
-    flags.paranoia_bits = PARANOID_PRAY; /* old prayconfirm=TRUE */
+    flags.paranoia_bits = PARANOID_PRAY|PARANOID_SWIM;
     flags.pile_limit = PILE_LIMIT_DFLT;  /* 5 */
     flags.runmode = RUN_LEAP;
     iflags.msg_history = 20;