pgsql: Move each SLRU's lwlocks to a separate tranche.

Move each SLRU's lwlocks to a separate tranche.

This makes it significantly easier to identify these lwlocks in
LWLOCK_STATS or Trace_lwlocks output.  It's also arguably better
from a modularity standpoint, since lwlock.c no longer needs to
know anything about the LWLock needs of the higher-level SLRU
facility.

Ildus Kurbangaliev, reviewd by Álvaro Herrera and by me.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/fe702a7b3f9f2bc5bf6d173166d7d55226af82c8

Modified Files
--------------
src/backend/access/transam/clog.c      |    2 +-
src/backend/access/transam/commit_ts.c |    2 +-
src/backend/access/transam/multixact.c |    4 ++--
src/backend/access/transam/slru.c      |   37 +++++++++++++++++++++-----------
src/backend/access/transam/subtrans.c  |    2 +-
src/backend/commands/async.c           |    2 +-
src/backend/storage/lmgr/lwlock.c      |   23 --------------------
src/backend/storage/lmgr/predicate.c   |    2 +-
src/include/access/slru.h              |   10 ++++++++-
9 files changed, 41 insertions(+), 43 deletions(-)