Something flaky in the "relfilenode mapping" infrastructure

Buildfarm member prairiedog thinks there's something unreliable about
commit f01d1ae3a104019d6d68aeff85c4816a275130b3:
http://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=prairiedog&dt=2014-03-27%2008%3A12%3A11

================== pgsql.13462/src/test/regress/regression.diffs ===================
*** /Users/buildfarm/bf-data/HEAD/pgsql.13462/src/test/regress/expected/alter_table.out Thu Mar 27 04:12:40 2014
--- /Users/buildfarm/bf-data/HEAD/pgsql.13462/src/test/regress/results/alter_table.out Thu Mar 27 04:52:02 2014
***************
*** 2333,2339 ****
) mapped;
incorrectly_mapped | have_mappings
--------------------+---------------
! 0 | t
(1 row)

-- Checks on creating and manipulation of user defined relations in
--- 2333,2339 ----
) mapped;
incorrectly_mapped | have_mappings
--------------------+---------------
! 1 | t
(1 row)

-- Checks on creating and manipulation of user defined relations in

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regards, tom lane