pgsql: Make pg_stat_file() use OUT parameters so that the user doesn't

Log Message:
-----------
Make pg_stat_file() use OUT parameters so that the user doesn't have to
remember the output parameter set for himself. It's a bit of a kluge
but fixing array_in to work in bootstrap mode looks worse.
I removed the separate pg_file_length() function, as it no longer has any
real notational advantage --- you can write (pg_stat_file(...)).length.

Modified Files:
--------------
pgsql/doc/src/sgml:
func.sgml (r1.279 -> r1.280)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.279&r2=1.280)
pgsql/src/backend/catalog:
system_views.sql (r1.18 -> r1.19)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/system_views.sql.diff?r1=1.18&r2=1.19)
pgsql/src/backend/utils/adt:
genfile.c (r1.3 -> r1.4)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/genfile.c.diff?r1=1.3&r2=1.4)
pgsql/src/include/catalog:
catversion.h (r1.297 -> r1.298)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.297&r2=1.298)
pg_proc.h (r1.382 -> r1.383)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.382&r2=1.383)