pgsql-server: Tweak palloc/repalloc to allow zero bytes to be requested,

Log Message:
-----------
Tweak palloc/repalloc to allow zero bytes to be requested, as per recent
proposal.  Eliminate several dozen now-unnecessary hacks to avoid palloc(0).
(It's likely there are more that I didn't find.)

Modified Files:
--------------
    pgsql-server/src/backend/access/nbtree:
        nbtree.c (r1.117 -> r1.118)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/nbtree/nbtree.c.diff?r1=1.117&r2=1.118)
    pgsql-server/src/backend/commands:
        analyze.c (r1.73 -> r1.74)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/analyze.c.diff?r1=1.73&r2=1.74)
        copy.c (r1.224 -> r1.225)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/copy.c.diff?r1=1.224&r2=1.225)
        tablecmds.c (r1.110 -> r1.111)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/tablecmds.c.diff?r1=1.110&r2=1.111)
        vacuum.c (r1.279 -> r1.280)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/vacuum.c.diff?r1=1.279&r2=1.280)
        vacuumlazy.c (r1.41 -> r1.42)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/vacuumlazy.c.diff?r1=1.41&r2=1.42)
    pgsql-server/src/backend/executor:
        execQual.c (r1.162 -> r1.163)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/executor/execQual.c.diff?r1=1.162&r2=1.163)
    pgsql-server/src/backend/optimizer/prep:
        prepunion.c (r1.113 -> r1.114)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/prep/prepunion.c.diff?r1=1.113&r2=1.114)
    pgsql-server/src/backend/optimizer/util:
        clauses.c (r1.173 -> r1.174)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/optimizer/util/clauses.c.diff?r1=1.173&r2=1.174)
    pgsql-server/src/backend/storage/freespace:
        freespace.c (r1.30 -> r1.31)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/freespace/freespace.c.diff?r1=1.30&r2=1.31)
    pgsql-server/src/backend/storage/lmgr:
        deadlock.c (r1.27 -> r1.28)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/lmgr/deadlock.c.diff?r1=1.27&r2=1.28)
        lock.c (r1.132 -> r1.133)

(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/lmgr/lock.c.diff?r1=1.132&r2=1.133)
    pgsql-server/src/backend/tcop:
        pquery.c (r1.79 -> r1.80)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/tcop/pquery.c.diff?r1=1.79&r2=1.80)
    pgsql-server/src/backend/utils/adt:
        name.c (r1.52 -> r1.53)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/adt/name.c.diff?r1=1.52&r2=1.53)
    pgsql-server/src/backend/utils/mmgr:
        README (r1.5 -> r1.6)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/mmgr/README.diff?r1=1.5&r2=1.6)
        mcxt.c (r1.44 -> r1.45)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/mmgr/mcxt.c.diff?r1=1.44&r2=1.45)
    pgsql-server/src/include/utils:
        memutils.h (r1.54 -> r1.55)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/utils/memutils.h.diff?r1=1.54&r2=1.55)
    pgsql-server/src/pl/plpgsql/src:
        pl_exec.c (r1.104 -> r1.105)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/pl/plpgsql/src/pl_exec.c.diff?r1=1.104&r2=1.105)
    pgsql-server/src/pl/plpython:
        plpython.c (r1.47 -> r1.48)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/pl/plpython/plpython.c.diff?r1=1.47&r2=1.48)