pgsql-server: Replace nested-BEGIN syntax for subtransactions with

Log Message:
-----------
Replace nested-BEGIN syntax for subtransactions with spec-compliant
SAVEPOINT/RELEASE/ROLLBACK-TO syntax. (Alvaro)
Cause COMMIT of a failed transaction to report ROLLBACK instead of
COMMIT in its command tag. (Tom)
Fix a few loose ends in the nested-transactions stuff.

Modified Files:
--------------
pgsql-server/src/backend/access/transam:
xact.c (r1.171 -> r1.172)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/transam/xact.c.diff?r1=1.171&r2=1.172)
pgsql-server/src/backend/executor:
spi.c (r1.120 -> r1.121)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/executor/spi.c.diff?r1=1.120&r2=1.121)
pgsql-server/src/backend/parser:
gram.y (r2.467 -> r2.468)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/gram.y.diff?r1=2.467&r2=2.468)
keywords.c (r1.151 -> r1.152)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/parser/keywords.c.diff?r1=1.151&r2=1.152)
pgsql-server/src/backend/storage/lmgr:
lmgr.c (r1.64 -> r1.65)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/storage/lmgr/lmgr.c.diff?r1=1.64&r2=1.65)
pgsql-server/src/backend/tcop:
postgres.c (r1.424 -> r1.425)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/tcop/postgres.c.diff?r1=1.424&r2=1.425)
utility.c (r1.220 -> r1.221)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/tcop/utility.c.diff?r1=1.220&r2=1.221)
pgsql-server/src/bin/psql:
tab-complete.c (r1.107 -> r1.108)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/bin/psql/tab-complete.c.diff?r1=1.107&r2=1.108)
pgsql-server/src/include/access:
xact.h (r1.66 -> r1.67)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/access/xact.h.diff?r1=1.66&r2=1.67)
pgsql-server/src/include/nodes:
parsenodes.h (r1.262 -> r1.263)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/nodes/parsenodes.h.diff?r1=1.262&r2=1.263)
pgsql-server/src/include/utils:
errcodes.h (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/utils/errcodes.h.diff?r1=1.12&r2=1.13)
pgsql-server/src/test/regress/expected:
transactions.out (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/test/regress/expected/transactions.out.diff?r1=1.6&r2=1.7)
pgsql-server/src/test/regress/sql:
transactions.sql (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/test/regress/sql/transactions.sql.diff?r1=1.6&r2=1.7)