Workaround for issue #37

This is a workaround for a problem with NHibernate in combination with
the Microsoft Oracle driver. See
http://thebasilet.blogspot.be/2009/07/nhibernate-oracle-clobs.html for
details
CustomType must set as string (#37)

Issue #37 was not completely fixed. The customtype must be set
with a stringvalue for the driver to see the change