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/save.c

@@ -46,6 +46,7 @@ static void zerocomp_bputc(int);
 #define HUP
 #endif
 
+/* the #save command */
 int
 dosave(void)
 {
@@ -69,7 +70,7 @@ dosave(void)
         } else
             (void) doredraw();
     }
-    return 0;
+    return ECMD_OK;
 }
 
 /* returns 1 if save successful */