Move includes out of anon namespace.

The included file was pulling in <cassert> and defining the Win32
assert implementation '_wassert' both inside and outside of the
anonymous namespace, leading to ambiguous function call errors on
static debug win32 builds.

See mailing list discussions:
http://public.kitware.com/pipermail/vtkusers/2016-April/094860.html
http://public.kitware.com/pipermail/vtkusers/2016-April/094854.html
http://public.kitware.com/pipermail/vtkusers/2016-April/094814.html