Small adjustment to pkgdiff to reduce diffs

[David Brownlee <abs%netbsd.org@localhost>]

In case anyone missed the commit message.

| Updated pkgtools/pkgdiff to 0.122
|
| Set TZ=UTC before calling diff to ensure everyone uses the same timezone
| to avoid spurious diffs in metadata, such as:
|
| < clock/clock.c.orig        1993-06-29 01:11:39.000000000 -0400
| ---
| > clock/clock.c.orig        1993-06-29 03:11:39.000000000 -0200

So the next time you run mkpatches you may find more diffs than
previously as timestamps in patches shift to UTC, but going forward
the number of spurious metadata diffs should reduce.