pgsql: Fix back-branch pg_regress scripts to try the "canonical"

Log Message:
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Fix back-branch pg_regress scripts to try the "canonical" expected file if we
tried a variant file from resultmap and it didn't match.  This is already done
in HEAD's C-code version, and is needed because OpenBSD has recently migrated
to a more standard handling of float underflow --- see buildfarm results
from emu.

Tags:
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REL7_3_STABLE

Modified Files:
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    pgsql/src/test/regress:
        pg_regress.sh (r1.28.2.1 -> r1.28.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.sh.diff?r1=1.28.2.1&r2=1.28.2.2)