Merge pull request #4758 from butane/uri_scheme_case

URI schemes are not case-sensitive
diff --git a/system/libraries/Trackback.php b/system/libraries/Trackback.php
index a9b2564..7222c00 100644
--- a/system/libraries/Trackback.php
+++ b/system/libraries/Trackback.php
@@ -370,7 +370,7 @@
 	{
 		$url = trim($url);
 
-		if (strpos($url, 'http') !== 0)
+		if (stripos($url, 'http') !== 0)
 		{
 			$url = 'http://'.$url;
 		}