pgsql: Preserve commit timestamps across clean restart

Preserve commit timestamps across clean restart

An oversight in setting the boundaries of known commit timestamps during
startup caused old commit timestamps to become inaccessible after a
server restart.

Author and reporter: Julien Rouhaud
Review, test code: Craig Ringer

Branch
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REL9_6_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/c8329f934e1bce2a47ca9127cb7cf704e070c278

Modified Files
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src/backend/access/transam/commit_ts.c      |   2 +
src/test/modules/commit_ts/t/004_restart.pl | 137 ++++++++++++++++++++++++++++
2 files changed, 139 insertions(+)