[ci skip] Change some log messages' level

'Class Loaded' type of messages flood log files when
log_threshold is set to 2 (debug). They're now logged
as 'info' level.

This is manually applying PR #1528, which was created
to do the same thing, but became outdated.
diff --git a/system/libraries/Upload.php b/system/libraries/Upload.php
index e022c43..3b0e044 100644
--- a/system/libraries/Upload.php
+++ b/system/libraries/Upload.php
@@ -296,7 +296,7 @@
 		$this->_mimes =& get_mimes();
 		$this->_CI =& get_instance();
 
-		log_message('debug', 'Upload Class Initialized');
+		log_message('info', 'Upload Class Initialized');
 	}
 
 	// --------------------------------------------------------------------