pgsql: Allow the planner's estimate of the fraction of a cursor's rows

[tgl(at)postgresql(dot)org (Tom Lane)]

Log Message:
-----------
Allow the planner's estimate of the fraction of a cursor's rows that will be
retrieved to be controlled through a GUC variable.

Robert Hell

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.176 -> r1.177)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.176&r2=1.177)
    pgsql/src/backend/optimizer/plan:
        planner.c (r1.232 -> r1.233)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planner.c?r1=1.232&r2=1.233)
    pgsql/src/backend/utils/misc:
        guc.c (r1.450 -> r1.451)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.450&r2=1.451)
        postgresql.conf.sample (r1.239 -> r1.240)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.239&r2=1.240)
    pgsql/src/include/optimizer:
        planmain.h (r1.107 -> r1.108)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/planmain.h?r1=1.107&r2=1.108)