adapted Carole_Bonnet2.py with the new modified method population_project.
Some upgrades of Simulation class

Followed the remarks of wednesday 22/05/2013 meeting.
Corrected the method to create age class.

The method now takes in account the population changes inside an age class.
renamed the method fill (DataCohorts.py) in _fill
Merge pull request #26 from jsantoul/master

Corrected the method to create age class.