pgsql: Fix inclusions in pgbench.c.

Fix inclusions in pgbench.c.

Apparently this was depending on pqsignal.h for <signal.h>.
Not sure why I didn't see the failure on my other machine.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/8c41cb695cc5f90eee3d2226ad09016381700ca7

Modified Files
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contrib/pgbench/pgbench.c |    1 +
1 files changed, 1 insertions(+), 0 deletions(-)