We can't keep a reference to data returned by libdb after a subsequent call to
any other libdb function on that DB.
Fixes a bug reported privately by Miho Taniyama (thanks!)... and hopefully
other hard-to-reproduce bugs.
stopgap measure to make vi recovery mostly functional on non-binary files.
The problem is that the db holding the recovery file can become corrupted,
in which case the data size of the line becomes huge. We use heuristics to
correct the size when we load a db in recovery mode. We could use a slightly
better heuristic (looking for ascii chars before correcting the length),
but it is not worth it. Another way would have been to trap the SEGV and
access data[len] and see if that worked, but that seemed exceedingly ugly.
