pgsql: Convert effective_cache_size to an integer, for better

Log Message:
-----------
Convert effective_cache_size to an integer, for better integration with
upcoming units feature.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.69 -> r1.70)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.69&r2=1.70)
pgsql/src/backend/optimizer/path:
costsize.c (r1.163 -> r1.164)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/costsize.c.diff?r1=1.163&r2=1.164)
pgsql/src/backend/utils/misc:
guc.c (r1.329 -> r1.330)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.329&r2=1.330)
pgsql/src/include/optimizer:
cost.h (r1.77 -> r1.78)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/optimizer/cost.h.diff?r1=1.77&r2=1.78)