implemented much of the general tab and behavior tab in the PreferencesDialog

app/dialog/preferences/preferences.cpp

@@ -89,6 +89,12 @@ void PreferencesDialog::AddBoolPair(QCheckBox *ui, bool *value, bool restart_req
 
 void PreferencesDialog::accept()
 {
+  foreach (PreferencesTab* tab, tabs_) {
+    if (!tab->Validate()) {
+      return;
+    }
+  }
+
   foreach (PreferencesTab* tab, tabs_) {
     tab->Accept();
   }