Bug#815089: libimage-exiftool-perl: extract timestamp hash/algo of signed+timestamped PDF

[Fulano Diego Perez]

i grepped through some other signed PDFs created from within Adobe
Acrobat, signed with differing CA certs and timestamp servers and
DigestAlgos - they all report the same md5 DigestValue...(?)

disappointingly, tests with LibreOffice Writer signed/timestamped PDFs
did not display a DigestValue. LO 5 can sign/timestamp exported PDFs but
only timestamp from a non-AUTH http[s] timestamp server

see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=810723

shall await mr exiftool's prognosis of DigestValue...