pgsql: On Darwin, refuse postmaster startup when multithreaded.

On Darwin, refuse postmaster startup when multithreaded.

The previous commit introduced its report at LOG level to avoid
surprises at minor release upgrade time.  Compel users deploying the
next major release to also deploy the reported workaround.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/2048e5b88198213ae15c4b59ddbe124f1a5dc2b7

Modified Files
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src/backend/postmaster/postmaster.c |    9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)