pgsql: Rename TransactionChain functions

Rename TransactionChain functions

We call this thing a "transaction block" everywhere except in a few
functions, where it is mysteriously called a "transaction chain".  In
the SQL standard, a transaction chain is something different.  So rename
these functions to match the common terminology.

Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/04700b685f31508036456bea4d92533e5ceee9d6

Modified Files
--------------
src/backend/access/transam/xact.c       | 28 ++++++++++++++--------------
src/backend/commands/cluster.c          |  2 +-
src/backend/commands/dbcommands.c       |  2 +-
src/backend/commands/discard.c          |  2 +-
src/backend/commands/portalcmds.c       |  2 +-
src/backend/commands/subscriptioncmds.c |  4 ++--
src/backend/commands/typecmds.c         |  2 +-
src/backend/commands/vacuum.c           |  4 ++--
src/backend/replication/walsender.c     |  6 +++---
src/backend/tcop/utility.c              | 30 +++++++++++++++---------------
src/backend/utils/misc/guc.c            | 10 +++++-----
src/backend/utils/time/snapmgr.c        |  2 +-
src/bin/psql/common.c                   |  2 +-
src/include/access/xact.h               |  8 ++++----
14 files changed, 52 insertions(+), 52 deletions(-)