Fix misspelled text with VoiceOver on 10.9

More in Apple's docs (Application Kit Release Notes for OS X v10.9,
section "New Accessibility constants").

Change-Id: I92fb6d552e86997bfc789723f32626d908d11419
Reviewed-on: https://gerrit.libreoffice.org/5831Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

vcl/aqua/source/a11y/aqua11ytextattributeswrapper.mm

@@ -294,6 +294,7 @@ using namespace ::rtl;
             switch(type) {
                 case ::com::sun::star::text::TextMarkupType::SPELLCHECK: {
                     [string addAttribute:NSAccessibilityMisspelledTextAttribute value:[NSNumber numberWithBool:YES] range:markupRange];
+                    [string addAttribute:@"AXMarkedMisspelled" value:[NSNumber numberWithBool:YES] range:markupRange];
                     break;
                 }
             }