Oid is defined as unsigned 32. On some Python implementations (probably
the ones where maxint = 2 ** 31) this can cause int overflow for large
values (see #961). On my 64 box it doesn't seem the case.

Oid handling was sloppy here and there (messages, casts...): trying to
use uint everywhere, and added a couple of helper macros to treat Oid
consistently.

Close #961.

    ag -l Copyright | xargs sed -i \
        "s/\(.*copyright (C) [0-9]\+\)\(-[0-9]\+\)\?\(.*\)/\1-$(date +%Y)\3/I"