NzImage now handles mipmaps

Added NzRenderer::SetClearColor(const Color&)
Added describe comment for pixel formats
Fixed NzPixelFormat conversion for RGBA4 and RGB5A1 types
Fixed NzRenderer::Clear prototype
Renamed NzLock to NzLockGuard
ResourceLoader's loaders are now tested from newest to oldest

include/Nazara/Core/LockGuard.hpp

@@ -0,0 +1,24 @@
+// Copyright (C) 2012 Jérôme Leclercq
+// This file is part of the "Nazara Engine".
+// For conditions of distribution and use, see copyright notice in Config.hpp
+
+#pragma once
+
+#ifndef NAZARA_LOCKGUARD_HPP
+#define NAZARA_LOCKGUARD_HPP
+
+#include <Nazara/Prerequesites.hpp>
+
+class NzMutex;
+
+class NAZARA_API NzLockGuard
+{
+	public:
+		NzLockGuard(NzMutex& mutex);
+		~NzLockGuard();
+
+	private:
+		NzMutex& m_mutex;
+};
+
+#endif // NAZARA_LOCKGUARD_HPP