pgsql: Make use of new list primitives list_append_unique and

Log Message:
-----------
Make use of new list primitives list_append_unique and list_concat_unique
where applicable.

Modified Files:
--------------
    pgsql/src/backend/optimizer/path:
        joinrels.c (r1.74 -> r1.75)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/joinrels.c.diff?r1=1.74&r2=1.75)
        pathkeys.c (r1.70 -> r1.71)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/pathkeys.c.diff?r1=1.70&r2=1.71)
    pgsql/src/backend/optimizer/prep:
        prepunion.c (r1.124 -> r1.125)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepunion.c.diff?r1=1.124&r2=1.125)
    pgsql/src/backend/optimizer/util:
        relnode.c (r1.70 -> r1.71)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/relnode.c.diff?r1=1.70&r2=1.71)
    pgsql/src/backend/parser:
        analyze.c (r1.322 -> r1.323)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/analyze.c.diff?r1=1.322&r2=1.323)
    pgsql/src/backend/rewrite:
        rewriteHandler.c (r1.155 -> r1.156)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/rewrite/rewriteHandler.c.diff?r1=1.155&r2=1.156)
    pgsql/src/backend/utils/adt:
        acl.c (r1.122 -> r1.123)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/acl.c.diff?r1=1.122&r2=1.123)
    pgsql/src/backend/utils/init:
        flatfiles.c (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/init/flatfiles.c.diff?r1=1.12&r2=1.13)