Logging should obey error_reporting() setting

If the php error level is not included in the current
error_reporting() setting, we should not log it.

Also, the log_threshold check is redundant, it's
already taken care of by the write_log() method.
diff --git a/system/core/Common.php b/system/core/Common.php
index 57374b0..cb99d05 100644
--- a/system/core/Common.php
+++ b/system/core/Common.php
@@ -524,21 +524,20 @@
 	{
 		$_error =& load_class('Exceptions', 'core');
 
-		// Should we display the error? We'll get the current error_reporting
+		// Should we ignore the error? We'll get the current error_reporting
 		// level and add its bits with the severity bits to find out.
-		// And respect display_errors
-		if (($severity & error_reporting()) === $severity && (bool) ini_get('display_errors') === TRUE)
+		if (($severity & error_reporting()) !== $severity)
+        {
+            return;
+        }
+        
+    	// Should we display the error?
+        if ((bool) ini_get('display_errors') === TRUE)
 		{
 			$_error->show_php_error($severity, $message, $filepath, $line);
 		}
 
-		// Should we log the error? No? We're done...
-		if (config_item('log_threshold') === 0)
-		{
-			return;
-		}
-
-		$_error->log_exception($severity, $message, $filepath, $line);
+	    $_error->log_exception($severity, $message, $filepath, $line);
 	}
 }