tlf_journal: convert to a branch if the journal is too long
tlf_journal: convert to a branch if the journal is too long

Issue: KBFS-1653

keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client