Preserve file access mode when backing up / restoring files

This change adds a fixed-size metadata block at the head of each file's content
entity.  The block is versioned, and fixed-size on the theory that it might be
nice to be able to recover the content (if not the full metadata) of the files
if we're ever confronted with data backed up some hypothetical future helper
that stored expanded metadata.

The net effect is that now on restore, we assign the same access mode to the
file that it originally had when backed up.

Also, some of the code was failing to properly free transient heap-based buffers
when it encountered errors.  This has been fixed with the addition of a tiny
stack-based object whose job it is to free() its designated pointer from its
destructor.

0 files changed, 0 insertions, 0 deletions