pgsql: Have crosstab variants treat NULL rowid as a category in its own

Log Message:
-----------
Have crosstab variants treat NULL rowid as a category in its own right,
per suggestion from Tom Lane. This fixes crash-bug reported by Stefan
Schwarzer.

Tags:
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REL8_1_STABLE

Modified Files:
--------------
    pgsql/contrib/tablefunc:
        tablefunc.c (r1.38.2.1 -> r1.38.2.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/tablefunc.c?r1=1.38.2.1&r2=1.38.2.2)
    pgsql/contrib/tablefunc/data:
        ct.data (r1.1 -> r1.1.12.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/data/ct.data?r1=1.1&r2=1.1.12.1)
    pgsql/contrib/tablefunc/expected:
        tablefunc.out (r1.12 -> r1.12.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/expected/tablefunc.out?r1=1.12&r2=1.12.2.1)
    pgsql/contrib/tablefunc/sql:
        tablefunc.sql (r1.11 -> r1.11.2.1)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/sql/tablefunc.sql?r1=1.11&r2=1.11.2.1)