Please make ObjectExtensions internal or define it in a custom namespace

[wjrogers]

In NPOI 2.5.5, you added these public extension methods in the System namepace: a3058a2. All consumers of NPOI are now forced to import these extension methods with the System namespace. Please consider changing the visibility of ObjectExtensions to internal or changing its namespace to e.g. NPOI.Util.

[tonyqus]

Sorry, it's my fault. This class definition is copied from stackoverflow.com or somewhere. You know Ctrl+C and Ctrl+V. I didn't pay much attention to the namespace at all. I'll change the namespace in the next release.