call file_reset() so that we don't accumulate errors from before.
PR/268: Account for different placement of [Content_types].xml by libreoffice.
PR/269: Note that the MBR 0xAA55 signature that originated in 1983 with
IBM PC DOS 2.0, is no more x86-specific (arm systems use it too). So call
the magic DOS/MBR as opposed to x86.
PR/280: Add ECDSA and PEM EC private keys.