[Distutils] add hash algorithm agility to RECORD

[Daniel Holth]

OK. Making MD5 optional in RECORD doesn't seem to be very
controversial any more, and it will make life easier for an entire
class of systems that compile md5() to produce a crash instead of a
message digest. It will not lull anyone into a false sense of security
or degrade performance.

The edit now suggests the installer pick from one of
hashlib.algorithms_guaranteed, currently:

{'sha1', 'sha224', 'sha384', 'sha256', 'sha512', 'md5'}

All valid arguments to hashlib.new(). The hash value is now either
empty, the md5 hexdigest, or the name of the hash, followed by =,
followed by the urlsafe-b64encode-nopad (base64 with trailing =
removed) of the digest.

Does an uninstaller exist that checks the hashes during uninstall?

Daniel Holth