libquota units

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I was somewhat surprised to learn that with libquota, qv_usage etc.
were still in units of what someone called "a constant of nature introduced
by DEC", e.g., 512-byte "blocks".
Given the fields are 64 bits wide, I would have expected them to be in
bytes instead, but there are probably reasons not do do that.
So, I would at least expect that to be documented or machine-readable.