Enhancing error message

plugins/check/index.php

@@ -91,9 +91,9 @@ if ($database->server_version<50500) echo('Warning: Lychee uses the GBK charset
 
 # About GD
 $gdVersion = gd_info();
-if (!$gdVersion['JPEG Support'])	$error .= ('Error: No GD without jpeg support' . PHP_EOL);
-if (!$gdVersion['PNG Support'])	  $error .= ('Error: No GD without png support' . PHP_EOL);
-if (!$gdVersion['GIF Read Support'] || !$gdVersion['GIF Create Support'])	  $error .= ('Error: No GD without full gif support' . PHP_EOL);
+if (!$gdVersion['JPEG Support'])	$error .= ('Error: PHP gd extension without jpeg support' . PHP_EOL);
+if (!$gdVersion['PNG Support'])	  $error .= ('Error: PHP gd extension without png support' . PHP_EOL);
+if (!$gdVersion['GIF Read Support'] || !$gdVersion['GIF Create Support'])	  $error .= ('Error: PHP gd extension without full gif support' . PHP_EOL);
 
 # Output
 if ($error==='')	echo('No critical problems found. Lychee should work without problems!' . PHP_EOL);