Fix upper/lower bound calculation in model constraint.

Backported from master.
Fixed a Schedule bug.

A combination of backwards generation and end-of-month convention
could result in missing or duplicated first dates.

Thanks to Nicholas Manganaro for the heads-up.
Update ChangeLog.
add upper and lower bound to projected constraint
Fix a few Doxygen comments.
Bump version number to 1.4.1.
Merge branch 'R01040x-branch' of https://github.com/lballabio/quantlib into R01040x-branch