pgsql-server: Issue a CHECKPOINT just after creating the regression

Log Message:
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Issue a CHECKPOINT just after creating the regression database. Without
this, it's hard to debug core-dump test failures, because WAL replay will
enthusiastically remove the core file (along with the rest of the
regression database directory). Per recent discussion, not to mention
bitter experience.

Modified Files:
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pgsql-server/src/test/regress:
pg_regress.sh (r1.46 -> r1.47)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/test/regress/pg_regress.sh.diff?r1=1.46&r2=1.47)