pgsql: Expose more cursor-related functionality in SPI: specifically,

Log Message:
-----------
Expose more cursor-related functionality in SPI: specifically, allow
access to the planner's cursor-related planning options, and provide new
FETCH/MOVE routines that allow access to the full power of those commands.
Small refactoring of planner(), pg_plan_query(), and pg_plan_queries()
APIs to make it convenient to pass the planning options down from SPI.

This is the core-code portion of Pavel Stehule's patch for scrollable
cursor support in plpgsql; I'll review and apply the plpgsql changes
separately.

Modified Files:
--------------
pgsql/doc/src/sgml:
spi.sgml (r1.55 -> r1.56)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/spi.sgml.diff?r1=1.55&r2=1.56)
pgsql/src/backend/commands:
copy.c (r1.279 -> r1.280)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/copy.c.diff?r1=1.279&r2=1.280)
explain.c (r1.160 -> r1.161)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/explain.c.diff?r1=1.160&r2=1.161)
portalcmds.c (r1.63 -> r1.64)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/portalcmds.c.diff?r1=1.63&r2=1.64)
prepare.c (r1.71 -> r1.72)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/prepare.c.diff?r1=1.71&r2=1.72)
pgsql/src/backend/executor:
functions.c (r1.114 -> r1.115)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/functions.c.diff?r1=1.114&r2=1.115)
spi.c (r1.175 -> r1.176)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/spi.c.diff?r1=1.175&r2=1.176)
pgsql/src/backend/optimizer/plan:
planner.c (r1.216 -> r1.217)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/planner.c.diff?r1=1.216&r2=1.217)
pgsql/src/backend/parser:
gram.y (r2.588 -> r2.589)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/gram.y.diff?r1=2.588&r2=2.589)
pgsql/src/backend/tcop:
postgres.c (r1.530 -> r1.531)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c.diff?r1=1.530&r2=1.531)
pgsql/src/backend/utils/cache:
plancache.c (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/plancache.c.diff?r1=1.6&r2=1.7)
pgsql/src/include/executor:
spi.h (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/executor/spi.h.diff?r1=1.60&r2=1.61)
pgsql/src/include/nodes:
parsenodes.h (r1.345 -> r1.346)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/nodes/parsenodes.h.diff?r1=1.345&r2=1.346)
pgsql/src/include/optimizer:
planner.h (r1.38 -> r1.39)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/planner.h.diff?r1=1.38&r2=1.39)
pgsql/src/include/tcop:
tcopprot.h (r1.88 -> r1.89)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/tcop/tcopprot.h.diff?r1=1.88&r2=1.89)