Registering LWTRANCHE_PARALLEL_HASH_JOIN

Hi,

I forgot to register a display name for LWTRANCHE_PARALLEL_HASH_JOIN,
the tranche ID used by the LWLock that Parallel Hash uses when handing
out chunks of memory.  Please see attached.

It's rare for this LWLock to show up in pg_stat_activity, but if you
stick pg_usleep(10000) into ExecParallelHashTupleAlloc() after the
lock is acquired (the slow path where a new 32KB chunk is needed) and
run some parallel hash joins, then you'll see that pg_stat_activity
reports that as "extension" in unpatched master.

-- 
Thomas Munro
http://www.enterprisedb.com