Restrict the teleportation notification to actual teleportations

teleds() is used for more than just teleportations, the teleportation message
was also given when mounting a steed.

Trying out a new bit flags method parameter design pattern.

src/dbridge.c

@@ -435,7 +435,7 @@ int xkill_flags, how;
                 if (enexto(&xy, etmp->ex, etmp->ey, etmp->edata)) {
                     pline("A %s force teleports you away...",
                           Hallucination ? "normal" : "strange");
-                    teleds(xy.x, xy.y, FALSE);
+                    teleds(xy.x, xy.y, TELEDS_NO_FLAGS);
                 }
                 /* otherwise on top of the drawbridge is the
                  * only viable spot in the dungeon, so stay there