scripts/filesize.sh doesn't follow symlinks.

Fixes #1316

We would like to check the file size instead of downloading indefinitely.
The file size is added in another copy of the manifest lines, which is
ignored by older autoupdater implementations.

The current autoupdater will only respect the last line for a given model
name, so we can add SHA256 checksums as long as they occur before the
corresponding SHA512 line.