pgsql: pg_upgrade: preserve the timestamp epoch

pg_upgrade:  preserve the timestamp epoch

This is useful for replication tools like Slony and Skytools.  This is a
backpatch of a74a4aa23bb95b590ff01ee564219d2eacea3706.

Report by Sergey Konoplev

Backpatch through 9.3

Branch
------
REL9_3_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/5724f491d2e02d6017e3101c9b7421437f2129e5

Modified Files
--------------
contrib/pg_upgrade/controldata.c |   16 ++++++++++------
contrib/pg_upgrade/pg_upgrade.c  |    8 ++++++--
contrib/pg_upgrade/pg_upgrade.h  |    1 +
3 files changed, 17 insertions(+), 8 deletions(-)