Bitcoin-Qt: fix known addressbook bugs

- add qSort() for cachedAddressTable, as qLowerBound() and qUpperBound()
  require the list to be in ascending order (see
  http://harmattan-dev.nokia.com/docs/library/html/qt4/qtalgorithms.html#qLowerBound)
- add a new check in AddressTableModel::setData() to just return, when no
  changes were made to a label or an address (prevents entry duplication
  issue)
- remove "rec->label = value.toString();" from
  AddressTableModel::setData() as the label gets updated by
  AddressTablePriv::updateEntry() anyway (seems @sipa added this line via
  https://github.com/bitcoin/bitcoin/commit/1025440184ef100a22d07c7bb543ee45cf169d64#L6R225)
- add another new check in AddressTableModel::setData() to just return, if
  a duplicate address was found (prevents address overwrite)
- add a new check to EditAddressDialog::setModel() to prevent setting an
  invalid model
- re-work the switch-case statement in AddressTableModel::accept() to
  always break (as return get's called anyway) and order the list to match
  the enum definition
- make accept() in editaddressdialog.h a public slot, which it should be
- misc small coding style changes

src/qt/addresstablemodel.cpp

@@ -69,6 +69,8 @@ public:
                                   QString::fromStdString(address.ToString())));
             }
         }
+        // qLowerBound() and qUpperBound() require our cachedAddressTable list to be sorted in asc order
+        qSort(cachedAddressTable.begin(), cachedAddressTable.end(), AddressTableEntryLessThan());
     }
 
     void updateEntry(const QString &address, const QString &label, bool isMine, int status)
@@ -208,7 +210,7 @@ QVariant AddressTableModel::data(const QModelIndex &index, int role) const
     return QVariant();
 }
 
-bool AddressTableModel::setData(const QModelIndex & index, const QVariant & value, int role)
+bool AddressTableModel::setData(const QModelIndex &index, const QVariant &value, int role)
 {
     if(!index.isValid())
         return false;
@@ -221,18 +223,36 @@ bool AddressTableModel::setData(const QModelIndex & index, const QVariant & valu
         switch(index.column())
         {
         case Label:
+            // Do nothing, if old label == new label
+            if(rec->label == value.toString())
+            {
+                editStatus = NO_CHANGES;
+                return false;
+            }
             wallet->SetAddressBookName(CBitcoinAddress(rec->address.toStdString()).Get(), value.toString().toStdString());
-            rec->label = value.toString();
             break;
         case Address:
+            // Do nothing, if old address == new address
+            if(CBitcoinAddress(rec->address.toStdString()) == CBitcoinAddress(value.toString().toStdString()))
+            {
+                editStatus = NO_CHANGES;
+                return false;
+            }
             // Refuse to set invalid address, set error status and return false
-            if(!walletModel->validateAddress(value.toString()))
+            else if(!walletModel->validateAddress(value.toString()))
             {
                 editStatus = INVALID_ADDRESS;
                 return false;
             }
+            // Check for duplicate addresses to prevent accidental deletion of addresses, if you try
+            // to paste an existing address over another address (with a different label)
+            else if(wallet->mapAddressBook.count(CBitcoinAddress(value.toString().toStdString()).Get()))
+            {
+                editStatus = DUPLICATE_ADDRESS;
+                return false;
+            }
             // Double-check that we're not overwriting a receiving address
-            if(rec->type == AddressTableEntry::Sending)
+            else if(rec->type == AddressTableEntry::Sending)
             {
                 {
                     LOCK(wallet->cs_wallet);
@@ -244,7 +264,6 @@ bool AddressTableModel::setData(const QModelIndex & index, const QVariant & valu
             }
             break;
         }
-
         return true;
     }
     return false;
@@ -262,7 +281,7 @@ QVariant AddressTableModel::headerData(int section, Qt::Orientation orientation,
     return QVariant();
 }
 
-Qt::ItemFlags AddressTableModel::flags(const QModelIndex & index) const
+Qt::ItemFlags AddressTableModel::flags(const QModelIndex &index) const
 {
     if(!index.isValid())
         return 0;
@@ -279,7 +298,7 @@ Qt::ItemFlags AddressTableModel::flags(const QModelIndex & index) const
     return retval;
 }
 
-QModelIndex AddressTableModel::index(int row, int column, const QModelIndex & parent) const
+QModelIndex AddressTableModel::index(int row, int column, const QModelIndex &parent) const
 {
     Q_UNUSED(parent);
     AddressTableEntry *data = priv->index(row);
@@ -345,6 +364,7 @@ QString AddressTableModel::addRow(const QString &type, const QString &label, con
     {
         return QString();
     }
+
     // Add entry
     {
         LOCK(wallet->cs_wallet);
@@ -353,7 +373,7 @@ QString AddressTableModel::addRow(const QString &type, const QString &label, con
     return QString::fromStdString(strAddress);
 }
 
-bool AddressTableModel::removeRows(int row, int count, const QModelIndex & parent)
+bool AddressTableModel::removeRows(int row, int count, const QModelIndex &parent)
 {
     Q_UNUSED(parent);
     AddressTableEntry *rec = priv->index(row);