journal_wipe — Wipe journal contents
int journal_wipe (journal_t * journal, int write);
Wipe out all of the contents of a journal, safely. This will produce
a warning if the journal contains any valid recovery information.
Must be called between journal_init_*() and journal_load.
If 'write' is non-zero, then we wipe out the journal on disk; otherwise we merely suppress recovery.