pipe-filter self-tests

[Simon Josefsson]

These self-tests appears to invoke the external command 'tr' which
doesn't work well under Windows, or does it?

Quoting http://autobuild.josefsson.org/gnulib/log-200908200817225767000.txt

./test-pipe-filter-gi1.exe: tr subprocess failed: No such file or directory
FAIL: test-pipe-filter-gi1.sh
./test-pipe-filter-ii1.exe: tr subprocess failed: No such file or directory
FAIL: test-pipe-filter-ii1.sh

It doesn't seem like the 'tr' tool is essential here, so maybe it could
execute a binary that is built by the self-test itself instead?  Or some
other expression that is more likely to work cross-platform.

FWIW, there are other failures too:

test-pipe-filter-gi2-main.c:132: assertion failed
FAIL: test-pipe-filter-gi2.sh
FAIL: test-pipe-filter-ii2.sh
test-pipe.c:79: assertion failed
test-pipe.sh: iteration 4 failed
test-pipe.c:79: assertion failed
test-pipe.sh: iteration 5 failed
test-pipe.c:79: assertion failed
test-pipe.sh: iteration 6 failed
test-pipe.c:79: assertion failed
test-pipe.sh: iteration 7 failed
FAIL: test-pipe.sh

/Simon