When switching between primary and alternate buffers, invoke -redraw after a...

When switching between primary and alternate buffers, invoke -redraw after a very short delay rather than immediately so there's no flash when an app wants to switch buffers, write a little, and immediatley switch back.

sources/PTYSession.m

@@ -5923,6 +5923,10 @@ static const NSTimeInterval kAntiIdleGracePeriod = 0.1;
     return self.guid;
 }
+- (void)screenScheduleRedrawSoon {
+    [self scheduleUpdateIn:kFastTimerIntervalSec];
+}
+
 - (void)screenNeedsRedraw {
     [self refreshAndStartTimerIfNeeded];
     [_textview updateNoteViewFrames];

sources/VT100Screen.m

@@ -3046,7 +3046,7 @@ static NSString *const kInlineFileBase64String = @"base64 string";  // NSMutable
     [self reloadMarkCache];
     [currentGrid_ markAllCharsDirty:YES];
-    [delegate_ screenNeedsRedraw];
+    [delegate_ screenScheduleRedrawSoon];
     commandStartX_ = commandStartY_ = -1;
 }
@@ -3088,7 +3088,7 @@ static NSString *const kInlineFileBase64String = @"base64 string";  // NSMutable
         [self reloadMarkCache];
         [currentGrid_ markAllCharsDirty:YES];
-        [delegate_ screenNeedsRedraw];
+        [delegate_ screenScheduleRedrawSoon];
     }
 }

sources/VT100ScreenDelegate.h

@@ -14,6 +14,9 @@
 // Screen contents have become dirty and should be redrawn right away.
 - (void)screenNeedsRedraw;
+// Schedule a refresh soon but not immediately.
+- (void)screenScheduleRedrawSoon;
+
 // Update window title, tab colors, and redraw view.
 - (void)screenUpdateDisplay:(BOOL)redraw;