lowering pg_regress privileges on Windows

From the "scratch a long running itch" department.

The attached ridiculously tiny patch solves the problem whereby while we
can run Postgres on Windows safely from an Administrator account, we
can't run run the regression tests from the same account, since it fails
on the tablespace test, the tablespace directory having been set up
without first having lowered privileges. The solution is to lower
pg_regress' privileges in the same way that we do with other binaries.
This is useful in setups like Appveyor where running under any other
account is ... difficult. For the cfbot Thomas has had to make the
script hack the schedule file to omit the tablespace test. This would
make that redundant.

I propose to backpatch this. It's close enough to a bug and the risk is
almost infinitely small.

cheers

andrew

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Andrew Dunstan https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services