[RFE] Teach hash-object to be able to choose signature types

Hi All,

I do not know whether this would be a good enhancement or micro project for someone (maybe me) to take on, but I'm wondering whether it might be a good idea to provide an option to hash-object to select the signature being computed. The use case begins when someone computes an object signature and stores a pre-converted SHA1 value. Then the repository is changed over to SHA256. When hash-object is next called, perhaps in a different clone or some other "next" scenario, the new signature will be SHA256, if I understand this correctly, and from the perspective of the someone in the use case, the signature mismatches.

What I am proposing is an option like --signature-type=SHA1|SHA256 or similar as an option to hash-object to allow the non-default signature to be selected explicitly. This is not entirely trivial looking through the code and presumably would require either teaching hash_object_file_literally or having a separate method to do the alternate calculation.

Thoughts? Regards, Randall

-- Brief whoami:
 NonStop developer since approximately 211288444200000000
 UNIX developer since approximately 421664400
-- In my real life, I talk too much.