pgsql: Make tap tests store postmaster logs and handle vpaths correctly

Make tap tests store postmaster logs and handle vpaths correctly

Given this it is possible that the buildfarm animals running these tests
will be able to capture adequate logging to allow diagnosis of failures.

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/da7db24cc22e3f0d96cfda134f3ed194279bb513

Modified Files
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src/Makefile.global.in          |    2 +-
src/bin/pg_rewind/RewindTest.pm |    6 +++---
src/test/perl/TestLib.pm        |   15 ++++++++++-----
3 files changed, 14 insertions(+), 9 deletions(-)