auto posting rules don't affect sibling files

[simonmichael]

Auto posting rules affect the whole current file and any parent or child file, but not sibling files (as with multiple -f options). The docs at https://hledger.org/journal.html#auto-postings-transaction-modifiers are not clear on this. Also auto posting rules' and periodic transaction rules' scope should be mentioned in the https://hledger.org/journal.html#directives reference table, probably.

Workaround for now: instead of multiple -f options, include all files in a single top level file and put auto posting rules there.

Related code: Hledger.Cli.Utils withJournalDo -> journalTransform -> journalAddForecast