Fix tix-port(8) diffs on non-English locales.

tix-port(8) parses the diff(1) output, to remove the "Only in …"
informational messages. As they are meant to be human-readable, not
machine-readable, they are translated to different languages, which
causes tix-port(8) to miss them. This patch sets LC_ALL=C for the diff
invocation, so that the messages are always in English.

tix/tix-port

@@ -317,7 +317,7 @@ diff_package() {(
   base=$(basename -- "$port")
   if [ -e "$base.upstream" ]; then
     announce "diff $base.upstream $base"
-    diff -Paur --no-dereference -- "$base.upstream" "$base" |
+    LC_ALL=C diff -Paur --no-dereference -- "$base.upstream" "$base" |
     sed -E -e '/^Only in.*$/d' -e 's/^((---|\+\+\+)[^\t]+)\t.*/\1/' \
     > "$base.patch"
     if [ ! -s "$base.patch" ]; then rm "$base.patch"; fi