Add datetime.date to protocol's simplejson encoder in order to be able to use dates in SQLAlchemy

[yves]

There is a special encoder in Protocol called MapFishJSONEncoder. This patch adds code to deal with dates.

[elemoine]

Yves, it may be that isinstance accepts a tuple as the 2nd arg:

if isinstance(obj, (decimal.Decimal, datetime.date, datetime.datetime)):

Could you check before commit please?

[yves]

(In [1295]) Added date/datetime capabilities to simplejson encoder Added hooks before_create/before_update closes #289 closes #290