pg_rewind and ssl test suites don't work if '.' is not in @INC

On my system running Debian stretch (= testing):

~/git-sandbox-pgsql/96stable/src/bin/pg_rewind (REL9_6_STABLE)$ make check
rm -rf '/home/heikki/git-sandbox-pgsql/96stable'/tmp_install
/bin/mkdir -p '/home/heikki/git-sandbox-pgsql/96stable'/tmp_install/log
make -C '../../..'
DESTDIR='/home/heikki/git-sandbox-pgsql/96stable'/tmp_install install

'/home/heikki/git-sandbox-pgsql/96stable'/tmp_install/log/install.log 2>&1

rm -rf
/home/heikki/git-sandbox-pgsql/96stable/src/bin/pg_rewind/tmp_check/log
cd . &&
TESTDIR='/home/heikki/git-sandbox-pgsql/96stable/src/bin/pg_rewind'
PATH="/home/heikki/git-sandbox-pgsql/96stable/tmp_install/home/heikki/pgsql.96stable/bin:$PATH"
LD_LIBRARY_PATH="/home/heikki/git-sandbox-pgsql/96stable/tmp_install/home/heikki/pgsql.96stable/lib"
PGPORT='65432'
PG_REGRESS='/home/heikki/git-sandbox-pgsql/96stable/src/bin/pg_rewind/../../../src/test/regress/pg_regress'
prove -I ../../../src/test/perl/ --verbose t/*.pl
t/001_basic.pl ............
1..8
Can't locate RewindTest.pm in @INC (you may need to install the
RewindTest module) (@INC contains:
/home/heikki/git-sandbox-pgsql/96stable/src/bin/pg_rewind/../../../src/test/perl
/etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.24.1
/usr/local/share/perl/5.24.1 /usr/lib/x86_64-linux-gnu/perl5/5.24
/usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.24
/usr/share/perl/5.24 /usr/local/lib/site_perl
/usr/lib/x86_64-linux-gnu/perl-base) at t/001_basic.pl line 6.
BEGIN failed--compilation aborted at t/001_basic.pl line 6.

That's not nice. Perl's @INC usually contains the current directory, and
those test suites rely on that, but that changed recently on Debian
stretch, and other distributions are likely to follow. There's more
information on this at https://www.debian.org/security/2016/dsa-3628.

I think we should fix this by the attached. Any better ideas?

I'm a bit surprised no-one else has reported this yet. Have I missed a
report?

- Heikki