Add root cause to exception when checking library

Author: ralfstx

bundles/com.eclipsesource.jshint.ui/src/com/eclipsesource/jshint/ui/internal/preferences/ui/JSHintPreferencePage.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2012 EclipseSource.
+ * Copyright (c) 2012, 2013 EclipseSource.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -215,7 +215,7 @@ private static void validateFile( File file ) throws IllegalArgumentException {
         inputStream.close();
       }
     } catch( Exception exception ) {
-      throw new IllegalArgumentException( "File is not a valid JSHint library" );
+      throw new IllegalArgumentException( "File is not a valid JSHint library", exception );
     }
   }