pgsql: Actually, we need to bump the format identifier on twophase files

Log Message:
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Actually, we need to bump the format identifier on twophase files
because of readjustment of 2PC rmgr IDs for flatfile removal.

Modified Files:
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    pgsql/src/backend/access/transam:
        twophase.c (r1.54 -> r1.55)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase.c?r1=1.54&r2=1.55)