[Qt] constify foreach uses where possible

- this doesn't replace BOOST_FOREACH, it just makes used arguments const
  where possible

src/qt/addressbookpage.cpp

@@ -254,8 +254,7 @@ void AddressBookPage::done(int retval)
     // Figure out which address was selected, and return it
     QModelIndexList indexes = table->selectionModel()->selectedRows(AddressTableModel::Address);
 
-    foreach (QModelIndex index, indexes)
-    {
+    foreach (const QModelIndex& index, indexes) {
         QVariant address = table->model()->data(index);
         returnValue = address.toString();
     }

src/qt/clientmodel.cpp

@@ -53,7 +53,7 @@ int ClientModel::getNumConnections(unsigned int flags) const
         return vNodes.size();
 
     int nNum = 0;
-    BOOST_FOREACH(CNode* pnode, vNodes)
+    BOOST_FOREACH(const CNode* pnode, vNodes)
         if (flags & (pnode->fInbound ? CONNECTIONS_IN : CONNECTIONS_OUT))
             nNum++;
 

src/qt/coincontroldialog.cpp

@@ -492,8 +492,7 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
     coinControl->ListSelected(vCoinControl);
     model->getOutputs(vCoinControl, vOutputs);
 
-    BOOST_FOREACH(const COutput& out, vOutputs)
-    {
+    BOOST_FOREACH(const COutput& out, vOutputs) {
         // unselect already spent, very unlikely scenario, this could happen
         // when selected are spent elsewhere, like rpc or another computer
         uint256 txhash = out.tx->GetHash();
@@ -691,8 +690,7 @@ void CoinControlDialog::updateView()
     map<QString, vector<COutput> > mapCoins;
     model->listCoins(mapCoins);
 
-    BOOST_FOREACH(PAIRTYPE(QString, vector<COutput>) coins, mapCoins)
-    {
+    BOOST_FOREACH(const PAIRTYPE(QString, vector<COutput>)& coins, mapCoins) {
         QTreeWidgetItem *itemWalletAddress = new QTreeWidgetItem();
         itemWalletAddress->setCheckState(COLUMN_CHECKBOX, Qt::Unchecked);
         QString sWalletAddress = coins.first;
@@ -719,8 +717,7 @@ void CoinControlDialog::updateView()
         double dPrioritySum = 0;
         int nChildren = 0;
         int nInputSum = 0;
-        BOOST_FOREACH(const COutput& out, coins.second)
-        {
+        BOOST_FOREACH(const COutput& out, coins.second) {
             int nInputSize = 0;
             nSum += out.tx->vout[out.i].nValue;
             nChildren++;

src/qt/receivecoinsdialog.cpp

@@ -185,8 +185,7 @@ void ReceiveCoinsDialog::on_showRequestButton_clicked()
         return;
     QModelIndexList selection = ui->recentRequestsView->selectionModel()->selectedRows();
 
-    foreach (QModelIndex index, selection)
-    {
+    foreach (const QModelIndex& index, selection) {
         on_recentRequestsView_doubleClicked(index);
     }
 }