transaction: reorder unlinking .hg/journal and .hg/journal.backupfiles...
transaction: reorder unlinking .hg/journal and .hg/journal.backupfiles
After this reordering, absence of '.hg/journal' just before starting
new transaction means also absence of '.hg/journal.backupfiles'.
In this case, all temporary files for preceding transaction should be
completely unlinked, and HG_PENDING doesn't cause unintentional
reading stalled temporary files in.
Otherwise, 'repo.transaction()' raises exception with "run 'hg
recover' to clean up transaction" hint.
