#1 patch to add an option to pad short files

[Frederick Bruckman]

Here's a patch to add an option to "pad" short files,
that is, to preserve the size for corrupted files,
which would otherwise be smaller than the originals.

It's only on option, because it hasn't proved as useful
as I'd hoped. For one thing, you don't know where the
missing line is, so if you're going to recover the file
with "par2", you may be destroying a good block. I'm
posting here anyway in the hope that it'll be useful to
someone for some purpose.

[Frederick Bruckman]

add option to pad short files