function date_increment_round() is declared in core datetime.module

Issue Summary

I just installed Date module onto latest Drupal 8 dev. It gave me an error indicating that the function date_increment_round() was already declared in core module datetime on the file datetime.module at the line 1039.

I have just removed the function declaration on the file date/date_api/date_api.module on the line 605 and the error is gone.