Merge branch 'mt/rot13-in-c'

Test portability improvements.

* mt/rot13-in-c:
  tests: use the new C rot13-filter helper to avoid PERL prereq
  t0021: implementation the rot13-filter.pl script in C
  t0021: avoid grepping for a Perl-specific string at filter output

diff --cc Makefile
Simple merge

diff --cc pkt-line.h
Simple merge