pgsql: Remove unnecessary opening of other relation in

Log Message:
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Remove unnecessary opening of other relation in RI_FKey_keyequal_upd_pk
and RI_FKey_keyequal_upd_fk, as well as no-longer-needed calls of
ri_BuildQueryKeyFull.  Aside from saving a few cycles, this avoids needless
deadlock risks when an update is not changing the columns that participate
in an RI constraint.  Per a gripe from Alexey Nalbat.

Back-patch to 8.3.  Earlier releases did have a need to open the other
relation due to the way in which they retrieved information about the RI
constraint, so this problem unfortunately can't easily be improved pre-8.3.

Tom Lane and Stephan Szabo

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        ri_triggers.c (r1.103 -> r1.104)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/ri_triggers.c?r1=1.103&r2=1.104)