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

src/Nazara/Core/LockGuard.cpp

@@ -0,0 +1,18 @@
+// 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
+
+#include <Nazara/Core/LockGuard.hpp>
+#include <Nazara/Core/Mutex.hpp>
+#include <Nazara/Core/Debug.hpp>
+
+NzLockGuard::NzLockGuard(NzMutex& mutex) :
+m_mutex(mutex)
+{
+	m_mutex.Lock();
+}
+
+NzLockGuard::~NzLockGuard()
+{
+	m_mutex.Unlock();
+}