About->Version info. Allow clipboard data to be available after closing KiCad.

Fixes a bug in GTK that erased the data on the clipboard after exiting KiCad.

common/dialog_about/dialog_about.cpp

@@ -483,6 +483,7 @@ void DIALOG_ABOUT::onCopyVersionInfo( wxCommandEvent& event )
     wxString msg_version = GetVersionInfoData( m_titleName );
 
     wxTheClipboard->SetData( new wxTextDataObject( msg_version ) );
+    wxTheClipboard->Flush(); // Allow clipboard data to be available after KiCad closes
     wxTheClipboard->Close();
     m_btCopyVersionInfo->SetLabel( _( "Copied..." ) );
 }