Bug 1159
Use interval start date (period from/since) to initialize first period.
This allows the offset of a period start to be specified
-p 'every 12 months from 2000-04-01'
will have periods
yyyy-04-01 to yyyy-03-31
....
If no from/since is specified for the period the first transaction date reported is used to initialize the period as before.
added test case regress/1159.test