Now works to use :maca on VimLeave auto command

To fix this the output queue is flushed before exiting a Vim process.
Also, the CloseWindowMsgID is added to the "unsafe" list so that other
unsafe messages (such as ExecuteActionMsgID) are not delayed until after
CloseWindowMsgID.

src/MacVim/MMBackend.m

@@ -589,10 +589,10 @@ static NSString *MMSymlinkWarningString =
 
     if ([connection isValid]) {
         @try {
-            int msgid = CloseWindowMsgID;
-            NSData *data = [NSData dataWithBytes:&msgid length:sizeof(int)];
-            NSArray *q = [NSArray arrayWithObjects:data, [NSData data], nil];
-            [frontendProxy processCommandQueue:q];
+            // Flush the entire queue in case a VimLeave autocommand added
+            // something to the queue.
+            [self queueMessage:CloseWindowMsgID data:nil];
+            [frontendProxy processCommandQueue:outputQueue];
         }
         @catch (NSException *e) {
             NSLog(@"Exception caught when sending CloseWindowMsgID: \"%@\"", e);

src/MacVim/MMVimController.m

@@ -1457,17 +1457,26 @@ isUnsafeMessage(int msgid)
     // example, UpdateTabBarMsgID may delete NSTabViewItem objects so it goes
     // on this list.
     static int unsafeMessages[] = { // REASON MESSAGE IS ON THIS LIST:
-        //OpenWindowMsgID,            //   Changes lots of state
-        UpdateTabBarMsgID,          //   May delete NSTabViewItem
-        RemoveMenuItemMsgID,        //   Deletes NSMenuItem
-        DestroyScrollbarMsgID,      //   Deletes NSScroller
-        ExecuteActionMsgID,         //   Impossible to predict
-        ShowPopupMenuMsgID,         //   Enters modal loop
-        ActivateMsgID,              //   ?
-        EnterFullscreenMsgID,       //   Modifies delegate of window controller
-        LeaveFullscreenMsgID,       //   Modifies delegate of window controller
+        //OpenWindowMsgID,            // Changes lots of state
+        UpdateTabBarMsgID,          // May delete NSTabViewItem
+        RemoveMenuItemMsgID,        // Deletes NSMenuItem
+        DestroyScrollbarMsgID,      // Deletes NSScroller
+        ExecuteActionMsgID,         // Impossible to predict
+        ShowPopupMenuMsgID,         // Enters modal loop
+        ActivateMsgID,              // ?
+        EnterFullscreenMsgID,       // Modifies delegate of window controller
+        LeaveFullscreenMsgID,       // Modifies delegate of window controller
+        CloseWindowMsgID,           // See note below
     };
 
+    // NOTE about CloseWindowMsgID: If this arrives at the same time as say
+    // ExecuteActionMsgID, then the "execute" message will be lost due to it
+    // being queued and handled after the "close" message has caused the
+    // controller to cleanup...UNLESS we add CloseWindowMsgID to the list of
+    // unsafe messages.  This is the _only_ reason it is on this list (since
+    // all that happens in response to it is that we schedule another message
+    // for later handling).
+
     int i, count = sizeof(unsafeMessages)/sizeof(unsafeMessages[0]);
     for (i = 0; i < count; ++i)
         if (msgid == unsafeMessages[i])