pgsql: Combine cmin and cmax fields of HeapTupleHeaders into a single

Log Message:
-----------
Combine cmin and cmax fields of HeapTupleHeaders into a single field, by
keeping private state in each backend that has inserted and deleted the same
tuple during its current top-level transaction.  This is sufficient since
there is no need to be able to determine the cmin/cmax from any other
transaction.  This gets us back down to 23-byte headers, removing a penalty
paid in 8.0 to support subtransactions.  Patch by Heikki Linnakangas, with
minor revisions by moi, following a design hashed out awhile back on the
pghackers list.

Modified Files:
--------------
    pgsql/src/backend/access/common:
        heaptuple.c (r1.114 -> r1.115)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/heaptuple.c.diff?r1=1.114&r2=1.115)
    pgsql/src/backend/access/heap:
        heapam.c (r1.227 -> r1.228)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c.diff?r1=1.227&r2=1.228)
    pgsql/src/backend/access/transam:
        xact.c (r1.233 -> r1.234)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xact.c.diff?r1=1.233&r2=1.234)
    pgsql/src/backend/utils/fmgr:
        fmgr.c (r1.103 -> r1.104)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/fmgr.c.diff?r1=1.103&r2=1.104)
    pgsql/src/backend/utils/time:
        Makefile (r1.11 -> r1.12)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/Makefile.diff?r1=1.11&r2=1.12)
    pgsql/src/include/access:
        htup.h (r1.90 -> r1.91)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/htup.h.diff?r1=1.90&r2=1.91)
    pgsql/src/include/catalog:
        catversion.h (r1.382 -> r1.383)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.382&r2=1.383)
    pgsql/src/include/storage:
        bufpage.h (r1.69 -> r1.70)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/bufpage.h.diff?r1=1.69&r2=1.70)
    pgsql/src/pl/plperl:
        plperl.c (r1.126 -> r1.127)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/plperl.c.diff?r1=1.126&r2=1.127)
    pgsql/src/pl/plpgsql/src:
        pl_comp.c (r1.112 -> r1.113)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_comp.c.diff?r1=1.112&r2=1.113)
        plpgsql.h (r1.84 -> r1.85)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/plpgsql.h.diff?r1=1.84&r2=1.85)
    pgsql/src/pl/plpython:
        plpython.c (r1.94 -> r1.95)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/plpython.c.diff?r1=1.94&r2=1.95)
    pgsql/src/pl/tcl:
        pltcl.c (r1.109 -> r1.110)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/tcl/pltcl.c.diff?r1=1.109&r2=1.110)
    pgsql/src/test/regress/expected:
        without_oid.out (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/without_oid.out.diff?r1=1.7&r2=1.8)
    pgsql/src/test/regress:
        parallel_schedule (r1.38 -> r1.39)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/parallel_schedule.diff?r1=1.38&r2=1.39)
        serial_schedule (r1.36 -> r1.37)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/serial_schedule.diff?r1=1.36&r2=1.37)
    pgsql/src/test/regress/sql:
        without_oid.sql (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/without_oid.sql.diff?r1=1.6&r2=1.7)

Added Files:
-----------
    pgsql/src/backend/utils/time:
        combocid.c (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/combocid.c?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/include/utils:
        combocid.h (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/combocid.h?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/test/regress/expected:
        combocid.out (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/combocid.out?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/test/regress/sql:
        combocid.sql (r1.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/combocid.sql?rev=1.1&content-type=text/x-cvsweb-markup)