pgsql-server: Fix subtransaction behavior for large objects, temp

Log Message:
-----------
Fix subtransaction behavior for large objects, temp namespace, files,
password/group files. Also allow read-only subtransactions of a read-write
parent, but not vice versa. These are the reasonably noncontroversial
parts of Alvaro's recent mop-up patch, plus further work on large objects
to minimize use of the TopTransactionResourceOwner.

Modified Files:
--------------
pgsql-server/src/backend/access/transam:
xact.c (r1.172 -> r1.173)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/transam/xact.c.diff?r1=1.172&r2=1.173)
pgsql-server/src/backend/catalog:
namespace.c (r1.67 -> r1.68)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/catalog/namespace.c.diff?r1=1.67&r2=1.68)
pgsql-server/src/backend/commands:
user.c (r1.141 -> r1.142)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/user.c.diff?r1=1.141&r2=1.142)
pgsql-server/src/backend/libpq:
be-fsstubs.c (r1.70 -> r1.71)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/libpq/be-fsstubs.c.diff?r1=1.70&r2=1.71)
pgsql-server/src/backend/storage/file:
fd.c (r1.109 -> r1.110)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/file/fd.c.diff?r1=1.109&r2=1.110)
pgsql-server/src/backend/storage/large_object:
inv_api.c (r1.102 -> r1.103)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/large_object/inv_api.c.diff?r1=1.102&r2=1.103)
pgsql-server/src/backend/storage/lmgr:
lmgr.c (r1.65 -> r1.66)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/lmgr/lmgr.c.diff?r1=1.65&r2=1.66)
pgsql-server/src/backend/utils/cache:
inval.c (r1.63 -> r1.64)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/cache/inval.c.diff?r1=1.63&r2=1.64)
pgsql-server/src/backend/utils/misc:
guc.c (r1.224 -> r1.225)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/misc/guc.c.diff?r1=1.224&r2=1.225)
pgsql-server/src/backend/utils/time:
tqual.c (r1.73 -> r1.74)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/utils/time/tqual.c.diff?r1=1.73&r2=1.74)
pgsql-server/src/bin/psql:
tab-complete.c (r1.108 -> r1.109)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/psql/tab-complete.c.diff?r1=1.108&r2=1.109)
pgsql-server/src/include/catalog:
namespace.h (r1.30 -> r1.31)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/catalog/namespace.h.diff?r1=1.30&r2=1.31)
pgsql-server/src/include/commands:
user.h (r1.22 -> r1.23)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/commands/user.h.diff?r1=1.22&r2=1.23)
pgsql-server/src/include/libpq:
be-fsstubs.h (r1.18 -> r1.19)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/libpq/be-fsstubs.h.diff?r1=1.18&r2=1.19)
pgsql-server/src/include/storage:
fd.h (r1.45 -> r1.46)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/storage/fd.h.diff?r1=1.45&r2=1.46)
large_object.h (r1.27 -> r1.28)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/storage/large_object.h.diff?r1=1.27&r2=1.28)
pgsql-server/src/include/utils:
inval.h (r1.32 -> r1.33)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/utils/inval.h.diff?r1=1.32&r2=1.33)