pgsql: Disallow committing a prepared transaction unless we are in the

Log Message:
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Disallow committing a prepared transaction unless we are in the same database
it was executed in.  Someday it might be nice to allow cross-DB commits, but
work would be needed in NOTIFY and perhaps other places.  Per Heikki.

Tags:
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REL8_2_STABLE

Modified Files:
--------------
    pgsql/src/backend/access/transam:
        twophase.c (r1.25 -> r1.25.2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase.c.diff?r1=1.25&r2=1.25.2.1)