Fix the automagic tuning of the number of unified diff context
lines. It was broken since previous commit to files/pkgdiff.
Also arguments '-u' and '-U NUM' to GNU diffutils 2.8.1, as seen
in NetBSD 2.0_STABLE and current, are not intended to be used
together. Hence only '-U NUM' is now specified. I did not reverted
to the '-u -NUM' form used before as it seems undesirable.
Please note that if PKGDIFF_FMT is specified in the environment,
for testing or debugging purposes, we skip the automagic tuning of
the number of unified diff context lines. The user probably wants
to try another diff format, as suggested in the commit log of
revision 1.12 of files/pkgdiff. So there is no point in adding '-U
NUM' to PKGDIFF_FMT: it may just not work. See:
$ diff -c -U 1 /dev/null /dev/null
diff: conflicting output style options
diff: Try `diff --help' for more information.
While here save a few basename(1) runs.
a47d96ceb9