date::day_of_week documentation is unhelpful

[russell.silva@…]

The Gregorian date documentation for the day_of_week method is unhelpful. It's not clear what the return type of the method is; it's not immediately obvious what a greg_day_of_week is. The example does not help, since it does not use the method at all. It turns out that the method returns an integer, but there is no documentation as to which day corresponds to which integer return value.

http://www.boost.org/doc/libs/1_43_0/doc/html/date_time/gregorian.html#date_time.gregorian.date_class

[Marshall Clow]

Duplicate of #4718