pgsql: Attempt to get plpython regression tests working again for MSVC

Attempt to get plpython regression tests working again for MSVC builds.

This has probably been broken for quite a long time. Buildfarm member
currawong's current results suggest that it's been broken since 9.1, so
backpatch this to that branch.

This only supports Python 2 - I will handle Python 3 separately, but
this is a fairly simple fix.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ef158312e96960bfbc802ceda58f432f6fd845eb

Modified Files
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src/tools/msvc/vcregress.pl |   11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)