Fix comparison function signature

This commit fixes build on CentOS 7 with GCC 4.8.5

src/qt/recentrequeststablemodel.cpp

@@ -12,8 +12,7 @@
 #include <clientversion.h>
 #include <streams.h>
 
-#include <algorithm>
-
+#include <utility>
 
 RecentRequestsTableModel::RecentRequestsTableModel(WalletModel *parent) :
     QAbstractTableModel(parent), walletModel(parent)
@@ -214,10 +213,10 @@ void RecentRequestsTableModel::updateDisplayUnit()
     updateAmountColumnTitle();
 }
 
-bool RecentRequestEntryLessThan::operator()(RecentRequestEntry &left, RecentRequestEntry &right) const
+bool RecentRequestEntryLessThan::operator()(const RecentRequestEntry& left, const RecentRequestEntry& right) const
 {
-    RecentRequestEntry *pLeft = &left;
-    RecentRequestEntry *pRight = &right;
+    const RecentRequestEntry* pLeft = &left;
+    const RecentRequestEntry* pRight = &right;
     if (order == Qt::DescendingOrder)
         std::swap(pLeft, pRight);
 

src/qt/recentrequeststablemodel.h

@@ -45,7 +45,7 @@ class RecentRequestEntryLessThan
 public:
     RecentRequestEntryLessThan(int nColumn, Qt::SortOrder fOrder):
         column(nColumn), order(fOrder) {}
-    bool operator()(RecentRequestEntry &left, RecentRequestEntry &right) const;
+    bool operator()(const RecentRequestEntry& left, const RecentRequestEntry& right) const;
 
 private:
     int column;