pgsql: Fix missing rows in query update a=..

Log Message:
-----------
Fix missing rows in query
update a=.. where a... with GiST index on column 'a'
Backpatch from 8.0 branch

Tags:
----
REL7_4_STABLE

Modified Files:
--------------
    pgsql/src/backend/access/gist:
        gist.c (r1.105 -> r1.105.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gist.c.diff?r1=1.105&r2=1.105.4.1)
        gistget.c (r1.36.4.1 -> r1.36.4.2)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistget.c.diff?r1=1.36.4.1&r2=1.36.4.2)
        gistscan.c (r1.47 -> r1.47.4.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistscan.c.diff?r1=1.47&r2=1.47.4.1)