Allow capitals in the middle of model names

Requested in #4059
diff --git a/system/core/Loader.php b/system/core/Loader.php
index 5de7a94..18e4c52 100644
--- a/system/core/Loader.php
+++ b/system/core/Loader.php
@@ -290,7 +290,7 @@
 			load_class('Model', 'core');
 		}
 
-		$model = ucfirst(strtolower($model));
+		$model = ucfirst($model);
 		if ( ! class_exists($model))
 		{
 			foreach ($this->_ci_model_paths as $mod_path)