Instead of renaming existing storage directories to a timestamped
format, create a timestamped directory in a temporary location and move
the individual files and folders inside storage directories to it. This
helps us with nested storage directories.

During the backup we create an intermediate copy of two directories:
builds and uploads. Instead of creating many small files with 'cp
-r', we now use tar (and fast gzip) to create single intermediate
files. This saves on disk IO and disk space while creating a backup.

This sidesteps problems with running 'chmod' on some CIFS mounts.

The backup restore code moves any existing uploads directory out of the
way before restoring the copy from the backup. If public/uploads was a
symlink, this move would replace the symlink. This commit avoids this
issue by first resolving any symlinks in the uploads path.