scripted-diff: Use the C++11 keyword nullptr to denote the pointer literal instead of the macro NULL

-BEGIN VERIFY SCRIPT-
sed -i 's/\<NULL\>/nullptr/g' src/*.cpp src/*.h src/*/*.cpp src/*/*.h src/qt/*/*.cpp src/qt/*/*.h src/wallet/*/*.cpp src/wallet/*/*.h src/support/allocators/*.h
sed -i 's/Prefer nullptr, otherwise SAFECOOKIE./Prefer NULL, otherwise SAFECOOKIE./g' src/torcontrol.cpp
sed -i 's/tor: Using nullptr authentication/tor: Using NULL authentication/g' src/torcontrol.cpp
sed -i 's/METHODS=nullptr/METHODS=NULL/g' src/test/torcontrol_tests.cpp src/torcontrol.cpp
sed -i 's/nullptr certificates/NULL certificates/g' src/qt/paymentserver.cpp
sed -i 's/"nullptr"/"NULL"/g' src/torcontrol.cpp src/test/torcontrol_tests.cpp
-END VERIFY SCRIPT-

src/support/lockedpool.cpp

@@ -28,7 +28,7 @@
 
 #include <algorithm>
 
-LockedPoolManager* LockedPoolManager::_instance = NULL;
+LockedPoolManager* LockedPoolManager::_instance = nullptr;
 std::once_flag LockedPoolManager::init_flag;
 
 /*******************************************************************************/
@@ -87,7 +87,7 @@ template <class Iterator, class Pair> bool extend(Iterator it, const Pair& other
 
 void Arena::free(void *ptr)
 {
-    // Freeing the NULL pointer is OK.
+    // Freeing the nullptr pointer is OK.
     if (ptr == nullptr) {
         return;
     }