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
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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(-)