pgsql: Clean up ill-advised attempt to invent a private set of Node tag

Clean up ill-advised attempt to invent a private set of Node tags.

Somebody thought it'd be cute to invent a set of Node tag numbers that were
defined independently of, and indeed conflicting with, the main tag-number
list. While this accidentally failed to fail so far, it would certainly
lead to trouble as soon as anyone wanted to, say, apply copyObject to these
node types. Clang was already complaining about the use of makeNode on
these tags, and I think quite rightly so. Fix by pushing these node
definitions into the mainstream, including putting replnodes.h where it
belongs.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/05e83968929f4ec1eba058fcae755fd2df98864e

Modified Files
--------------
src/backend/replication/repl_gram.y | 4 +-
src/backend/replication/walsender.c | 6 ++--
src/include/nodes/nodes.h | 7 ++++
src/include/nodes/replnodes.h | 52 ++++++++++++++++++++++++++++
src/include/replication/basebackup.h | 4 +-
src/include/replication/replnodes.h | 62 ----------------------------------
6 files changed, 66 insertions(+), 69 deletions(-)