* src/Utils.py: probably_alive now takes date rather than year
* src/gen/proxy/living.py: create date from year
* src/gen/lib/date.py: added methods to do date math
and return Date object (set_yr_mon_day_offset, copy_offset_ymd)
* src/plugins/Calendar.py: updated to use probably alive date
* src/Filters/Rules/Person/_ProbablyAlive.py: parse entry as date
svn: r9379
