pgsql: Avoid odd portability problem in TestLib.pm's slurp_file functio

Avoid odd portability problem in TestLib.pm's slurp_file function.

For unclear reasons, this function doesn't always read the expected data
in some old Perl versions.  Rewriting it to avoid use of ARGV seems to
dodge the problem, and this version is clearer anyway if you ask me.

In passing, also improve error message in adjacent append_to_file function.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/56a79a5ae9fe1426b07f8ad986777829f19b4437

Modified Files
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src/test/perl/TestLib.pm |    7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)