pgsql: Lower privilege level of programs calling regression_main

Lower privilege level of programs calling regression_main

On Windows this mean that the regression tests can now safely and
successfully run as Administrator, which is useful in situations like
Appveyor. Elsewhere it's a no-op.

Backpatch to 9.5 - this is harder in earlier branches and not worth the
trouble.

Discussion: https://postgr.es/m/650b0c29-9578-8571-b1d2-550d7f89f307@2ndQuadrant.com

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/42a93da25a5ce8e3937eabbf12f2be6837ab7e82

Modified Files
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src/test/regress/pg_regress.c | 2 ++
1 file changed, 2 insertions(+)