Wrong window size on MacOS

[lkesteloot]

On MacOS the window is not tall enough, because the passed-in rectangle (the size of the image) is used for the entire window, including the title bar. I don't know why, since the API for NSWindow calls the parameter contentRect. You have to convert from contentRect to frameRect yourself in mfb_open():

        NSRect rectangle = NSMakeRect(0, 0, width, height);
-       window_ = [[OSXWindow alloc] initWithContentRect:rectangle styleMask:styles backing:NSBackingStoreBuffered defer:NO];
+        NSRect frameRect = [NSWindow frameRectForContentRect:rectangle styleMask:styles];
+       window_ = [[OSXWindow alloc] initWithContentRect:frameRect styleMask:styles backing:NSBackingStoreBuffered defer:NO];

[emoon]

Thanks! Can you create a PR with this change?