Make extended commands return defined flags

Instead of returning 0 or 1, we'll now use ECMD_OK or ECMD_TURN.
These have the same meaning as the hardcoded numbers; ECMD_TURN
means the command uses a turn.

In future, could add eg. a flag denoting "user cancelled command"
or "command failed", and should clear eg. the cmdq.

Mostly this was simply replacing return values with the defines
in the extended commands, so hopefully I didn't break anything.

src/end.c

@@ -340,7 +340,7 @@ done2(void)
             u.uinvulnerable = FALSE; /* avoid ctrl-C bug -dlc */
             u.usleep = 0;
         }
-        return 0;
+        return ECMD_OK;
     }
 #if (defined(UNIX) || defined(VMS) || defined(LATTICE))
     if (wizard) {
@@ -369,7 +369,7 @@ done2(void)
 #ifndef LINT
     done(QUIT);
 #endif
-    return 0;
+    return ECMD_OK;
 }
 
 #ifndef NO_SIGNAL