mark billingDb to be forbidden

It seems billingDb was used at least until 1.9.12 instead of the current
billingLogsDir but never marked as forbidden.

* Mark billingDb to be forbidden and replaced by billingLogsDir.

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Merge branch 'master' into legacy-billing-options
mark more legacy options to be obsolete

It seems billingDbCommitRows and billingDbCommitIntervalInMilliseconds were used
at least until 1.9.12 and later replaced by similar options.
I use "obsolete" as both options seem to be not critical.

* Mark billingDbCommitRows to be obsolete and replaced by
  billingMaxInsertsBeforeCommit.
* Mark billingDbCommitIntervalInMilliseconds to be obsolete and replaced by
  billingMaxTimeBeforeCommitInSecs.

Require-notes: no
Require-book: no

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Merge pull request #32 from calestyo/legacy-billing-options

Mark legacy billing options as forbidden or obsolete.

Acked-by: Gerd Behrmann <behrmann@nordu.net>
Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>