Add a defensive check in CI_Loader::_ci_load()

Prevents possible internal variable overwrites when loading views
diff --git a/system/core/Loader.php b/system/core/Loader.php
index 62781a7..c742ae7 100644
--- a/system/core/Loader.php
+++ b/system/core/Loader.php
@@ -936,6 +936,14 @@
 		 */
 		if (is_array($_ci_vars))
 		{
+			foreach (array_keys($_ci_vars) as $key)
+			{
+				if (strncmp($key, '_ci_', 4) === 0)
+				{
+					unset($_ci_vars[$key]);
+				}
+			}
+
 			$this->_ci_cached_vars = array_merge($this->_ci_cached_vars, $_ci_vars);
 		}
 		extract($this->_ci_cached_vars);