Use case-insensitive comparison in Qt wxComboBox and wxChoice

Define LexicalSortProxyModel to use the same sort order in wxQt as in
the other ports.

src/qt/choice.cpp

@@ -10,11 +10,39 @@
 
 #include "wx/choice.h"
 #include "wx/qt/private/winevent.h"
+
 #include <QtWidgets/QComboBox>
+#include <QtCore/QSortFilterProxyModel>
 
 namespace
 {
 
+class LexicalSortProxyModel : public QSortFilterProxyModel
+{
+public:
+    bool lessThan( const QModelIndex &left, const QModelIndex &right ) const wxOVERRIDE
+    {
+        const QVariant leftData = sourceModel()->data( left );
+        const QVariant rightData = sourceModel()->data( right );
+
+        if ( leftData.type() != QVariant::String )
+            return false;
+
+        int insensitiveResult = QString::compare(
+                leftData.value<QString>(),
+                rightData.value<QString>(),
+                Qt::CaseInsensitive );
+
+        if ( insensitiveResult == 0 )
+        {
+            return QString::compare( leftData.value<QString>(),
+                                     rightData.value<QString>() ) < 0;
+        }
+
+        return insensitiveResult < 0;
+    }
+};
+
 class wxQtChoice : public wxQtEventSignalHandler< QComboBox, wxChoice >
 {
 public:
@@ -47,6 +75,14 @@ wxChoice::wxChoice() :
 {
 }
 
+void wxChoice::InitialiseSort(QComboBox *combo)
+{
+    QSortFilterProxyModel *proxyModel = new LexicalSortProxyModel();
+    proxyModel->setSourceModel(combo->model());
+    combo->model()->setParent(proxyModel);
+    combo->setModel(proxyModel);
+}
+
 
 wxChoice::wxChoice( wxWindow *parent, wxWindowID id,
         const wxPoint& pos,
@@ -95,6 +131,8 @@ bool wxChoice::Create( wxWindow *parent, wxWindowID id,
 {
     m_qtComboBox = new wxQtChoice( parent, this );
 
+    InitialiseSort(m_qtComboBox);
+
     while ( n-- > 0 )
         m_qtComboBox->addItem( wxQtConvertString( *choices++ ));