Wiindow Aggregate function

Hi All

I post this question to Stack Overflow the other day and ended up providing
my own solution.

<goog_2005557492>
http://stackoverflow.com/questions/38378971/postgresql-running-totals-with-groups-missing-data-and-outer-joins

However, the solution is incomplete. I need for arbitrary time intervals
as described in my edit.

Any help would be greatly appreciated.

Herby