MB-100: Fix build error on windows.

On windows, std::tr1 doesn't have definition for
static_pointer_cast

Change-Id: If978d165bd55833fde34e03a4e650eeb94166db5
Reviewed-on: http://review.couchbase.org/28149
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>