Avoid explicit deletion of preview window: this crashes on the mac. Use deleteonclose flag instead

src/qtgui/preview_w.cpp

@@ -99,6 +99,8 @@ static void trimwildcards(string& elt)
 void Preview::init()
 {
     LOGDEB("Preview::init\n");
+    setAttribute(Qt::WA_DeleteOnClose);
+    
     // Create the first tab (the tab widget is created with one
     // initial tab for ease of use in designer, we remove it).
     addEditorTab();

src/qtgui/rclm_preview.cpp

@@ -38,7 +38,6 @@ void RclMain::previewClosed(Preview *w)
     } else {
         LOGDEB("Old preview closed\n");
     }
-    delete w;
 }
 
 // Document up to date check. The main problem we try to solve is

src/qtgui/snippets_w.cpp

@@ -104,6 +104,7 @@ void SnippetsW::init()
     connect(prevPB, SIGNAL(clicked()), this, SLOT(slotEditFindPrevious()));
 
 
+    // Get rid of the placeholder widget created from the .ui
     delete browserw;
 #if defined(USING_WEBKIT)
     browserw = new QWebView(this);