pgsql: Fix portability and translatability issues in commit 64f85894a.

Fix portability and translatability issues in commit 64f85894a.

Compilation failed for lack of an #ifdef on builds without
pg_strong_random(). Also fix relevant error messages to meet
project style guidelines.

Fabien Coelho, further adjusted by me

Discussion: /messages/by-id/32390.1522464534@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5635c7aa678804292fe47bceab5b3f4dae5f39f9

Modified Files
--------------
src/bin/pgbench/pgbench.c | 31 +++++++++++++++++++++---------
src/bin/pgbench/t/002_pgbench_no_server.pl | 3 ++-
2 files changed, 24 insertions(+), 10 deletions(-)