pgsql: Redefine the lp_flags field of item pointers as having four

Log Message:
-----------
Redefine the lp_flags field of item pointers as having four states, rather
than two independent bits (one of which was never used in heap pages anyway,
or at least hadn't been in a very long time).  This gives us flexibility to
add the HOT notions of redirected and dead item pointers without requiring
anything so klugy as magic values of lp_off and lp_len.  The state values
are chosen so that for the states currently in use (pre-HOT) there is no
change in the physical representation.

Modified Files:
--------------
    pgsql/contrib/pageinspect:
        btreefuncs.c (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pageinspect/btreefuncs.c?r1=1.4&r2=1.5)
        heapfuncs.c (r1.1 -> r1.2)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pageinspect/heapfuncs.c?r1=1.1&r2=1.2)
    pgsql/contrib/pgstattuple:
        pgstattuple.c (r1.28 -> r1.29)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgstattuple/pgstattuple.c?r1=1.28&r2=1.29)
    pgsql/src/backend/access/gin:
        ginentrypage.c (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginentrypage.c?r1=1.7&r2=1.8)
        ginvacuum.c (r1.15 -> r1.16)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginvacuum.c?r1=1.15&r2=1.16)
        ginxlog.c (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginxlog.c?r1=1.7&r2=1.8)
    pgsql/src/backend/access/gist:
        gist.c (r1.145 -> r1.146)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gist.c?r1=1.145&r2=1.146)
        gistget.c (r1.66 -> r1.67)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistget.c?r1=1.66&r2=1.67)
        gistutil.c (r1.22 -> r1.23)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistutil.c?r1=1.22&r2=1.23)
        gistvacuum.c (r1.30 -> r1.31)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistvacuum.c?r1=1.30&r2=1.31)
    pgsql/src/backend/access/hash:
        hash.c (r1.95 -> r1.96)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/hash/hash.c?r1=1.95&r2=1.96)
        hashinsert.c (r1.45 -> r1.46)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/hash/hashinsert.c?r1=1.45&r2=1.46)
        hashovfl.c (r1.58 -> r1.59)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/hash/hashovfl.c?r1=1.58&r2=1.59)
        hashpage.c (r1.68 -> r1.69)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/hash/hashpage.c?r1=1.68&r2=1.69)
    pgsql/src/backend/access/heap:
        heapam.c (r1.239 -> r1.240)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c?r1=1.239&r2=1.240)
        hio.c (r1.65 -> r1.66)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/hio.c?r1=1.65&r2=1.66)
        rewriteheap.c (r1.5 -> r1.6)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/rewriteheap.c?r1=1.5&r2=1.6)
    pgsql/src/backend/access/nbtree:
        README (r1.17 -> r1.18)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/README?r1=1.17&r2=1.18)
        nbtinsert.c (r1.158 -> r1.159)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtinsert.c?r1=1.158&r2=1.159)
        nbtpage.c (r1.102 -> r1.103)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtpage.c?r1=1.102&r2=1.103)
        nbtsort.c (r1.111 -> r1.112)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtsort.c?r1=1.111&r2=1.112)
        nbtutils.c (r1.85 -> r1.86)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtutils.c?r1=1.85&r2=1.86)
        nbtxlog.c (r1.44 -> r1.45)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtxlog.c?r1=1.44&r2=1.45)
    pgsql/src/backend/commands:
        sequence.c (r1.144 -> r1.145)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/sequence.c?r1=1.144&r2=1.145)
        trigger.c (r1.218 -> r1.219)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c?r1=1.218&r2=1.219)
        vacuum.c (r1.357 -> r1.358)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c?r1=1.357&r2=1.358)
        vacuumlazy.c (r1.94 -> r1.95)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c?r1=1.94&r2=1.95)
    pgsql/src/backend/executor:
        nodeBitmapHeapscan.c (r1.18 -> r1.19)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeBitmapHeapscan.c?r1=1.18&r2=1.19)
    pgsql/src/backend/storage/page:
        bufpage.c (r1.72 -> r1.73)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/page/bufpage.c?r1=1.72&r2=1.73)
    pgsql/src/include/storage:
        bufpage.h (r1.72 -> r1.73)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/bufpage.h?r1=1.72&r2=1.73)
        itemid.h (r1.27 -> r1.28)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/itemid.h?r1=1.27&r2=1.28)