Close database when done

This prevents messages 'Connection reset by peer' in the postgresql log file.

It might have benefits for other databases as well ?

TileGenerator.cpp

@@ -202,6 +202,7 @@ TileGenerator::TileGenerator():
 
 TileGenerator::~TileGenerator()
 {
+	closeDb();
 }
 
 void TileGenerator::setSilenceSuggestion(unsigned flags)
@@ -557,6 +558,7 @@ void TileGenerator::generate(const std::string &input, const std::string &output
 	if (!m_drawObjects.empty()) {
 		renderDrawObjects();
 	}
+	closeDb();
 	if (progressIndicator)
 	    cout << "Writing image...\r" << std::flush;
 	writeImage(output);
@@ -859,6 +861,14 @@ void TileGenerator::openDb(const std::string &input)
 		throw std::runtime_error(((std::string) "World uses backend '") + m_backend + ", which was not enabled at compile-time.");
 }
 
+void TileGenerator::closeDb()
+{
+	if (m_db) {
+		delete m_db;
+		m_db = NULL;
+	}
+}
+
 void TileGenerator::loadBlocks()
 {
 	int mapXMin, mapXMax;

TileGenerator.h

@@ -162,6 +162,7 @@ private:
 	std::string getWorldDatabaseBackend(const std::string &input);
 	int getMapChunkSize(const std::string &input);
 	void openDb(const std::string &input);
+	void closeDb();
 	void sanitizeParameters(void);
 	void loadBlocks();
 	void createImage();

db.h

@@ -12,6 +12,7 @@
 
 class DB {
 public:
+	virtual ~DB() {}
 	typedef std::pair<BlockPos, ustring> Block;
 	typedef std::vector<BlockPos>  BlockPosList;
 	virtual const BlockPosList &getBlockPosList()=0;