pgsql: Create the planner mechanism for optimizing simple MIN and MAX

Log Message:
-----------
Create the planner mechanism for optimizing simple MIN and MAX queries
into indexscans on matching indexes. For the moment, it only handles
int4 and text datatypes; next step is to add a column to pg_aggregate
so that all MIN/MAX aggregates can be handled. Per my recent proposal.

Modified Files:
--------------
pgsql/src/backend/optimizer/path:
indxpath.c (r1.172 -> r1.173)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/indxpath.c.diff?r1=1.172&r2=1.173)
pgsql/src/backend/optimizer/plan:
Makefile (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/Makefile.diff?r1=1.12&r2=1.13)
planner.c (r1.183 -> r1.184)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planner.c.diff?r1=1.183&r2=1.184)
subselect.c (r1.95 -> r1.96)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/subselect.c.diff?r1=1.95&r2=1.96)
pgsql/src/backend/utils/cache:
lsyscache.c (r1.122 -> r1.123)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/lsyscache.c.diff?r1=1.122&r2=1.123)
pgsql/src/include/optimizer:
paths.h (r1.80 -> r1.81)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/paths.h.diff?r1=1.80&r2=1.81)
planmain.h (r1.80 -> r1.81)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/planmain.h.diff?r1=1.80&r2=1.81)
subselect.h (r1.23 -> r1.24)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/subselect.h.diff?r1=1.23&r2=1.24)
pgsql/src/include/utils:
lsyscache.h (r1.96 -> r1.97)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/lsyscache.h.diff?r1=1.96&r2=1.97)
pgsql/src/test/regress/expected:
aggregates.out (r1.11 -> r1.12)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/aggregates.out.diff?r1=1.11&r2=1.12)
create_index.out (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/create_index.out.diff?r1=1.14&r2=1.15)
pgsql/src/test/regress/sql:
aggregates.sql (r1.9 -> r1.10)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/aggregates.sql.diff?r1=1.9&r2=1.10)
create_index.sql (r1.13 -> r1.14)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/create_index.sql.diff?r1=1.13&r2=1.14)

Added Files:
-----------
pgsql/src/backend/optimizer/plan:
planagg.c (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planagg.c?rev=1.1&content-type=text/x-cvsweb-markup)