pgsql: In pg_upgrade, create a script to incrementally generate more ac

In pg_upgrade, create a script to incrementally generate more accurate
optimizer statistics so the cluster can be made available sooner.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/faec2815c8ea9d50da503896bb55222aabcc9741

Modified Files
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contrib/pg_upgrade/check.c | 144 ++++++++++++++++++++++++++++++++++++--
contrib/pg_upgrade/pg_upgrade.c | 6 ++-
contrib/pg_upgrade/pg_upgrade.h | 4 +-
3 files changed, 144 insertions(+), 10 deletions(-)