[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to do the same thing, but became outdated.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/core/Output.php b/system/core/Output.php
index beac6b3..6b9a33d 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -141,7 +141,7 @@
 		// Get mime types for later
 		$this->mimes =& get_mimes();
 
-		log_message('debug', 'Output Class Initialized');
+		log_message('info', 'Output Class Initialized');
 	}
 
 	// --------------------------------------------------------------------
@@ -491,7 +491,7 @@
 			}
 
 			echo $output;
-			log_message('debug', 'Final output sent to browser');
+			log_message('info', 'Final output sent to browser');
 			log_message('debug', 'Total execution time: '.$elapsed);
 			return;
 		}
@@ -528,7 +528,7 @@
 			echo $output; // Send it to the browser!
 		}
 
-		log_message('debug', 'Final output sent to browser');
+		log_message('info', 'Final output sent to browser');
 		log_message('debug', 'Total execution time: '.$elapsed);
 	}