pgsql: Change xlog.h to xlogdefs.h in bufpage.h, and fix fallout.

Log Message:
-----------
Change xlog.h to xlogdefs.h in bufpage.h, and fix fallout.

Modified Files:
--------------
    pgsql/src/backend/nodes:
        print.c (r1.87 -> r1.88)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/nodes/print.c?r1=1.87&r2=1.88)
    pgsql/src/backend/postmaster:
        postmaster.c (r1.557 -> r1.558)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c?r1=1.557&r2=1.558)
    pgsql/src/backend/utils/adt:
        domains.c (r1.6 -> r1.7)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/domains.c?r1=1.6&r2=1.7)
    pgsql/src/backend/utils/fmgr:
        fmgr.c (r1.119 -> r1.120)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/fmgr.c?r1=1.119&r2=1.120)
    pgsql/src/include/access:
        gin.h (r1.20 -> r1.21)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/gin.h?r1=1.20&r2=1.21)
        heapam.h (r1.134 -> r1.135)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/heapam.h?r1=1.134&r2=1.135)
        nbtree.h (r1.118 -> r1.119)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/nbtree.h?r1=1.118&r2=1.119)
    pgsql/src/include/storage:
        bufpage.h (r1.79 -> r1.80)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/bufpage.h?r1=1.79&r2=1.80)