Fail when include date api in date 2.0rc

We will see include error when using date 2.0.

warning: include_once(sites/all/modules/date/date.inc) [function.include-once]: failed to open stream: No such file or directory in /usr/local/www/feed.funmakr.com/sites/all/modules/feedapi/feedapi_mapper/mappers/feedapi_mapper_date.inc on line 29.