pgsql: Remove the limit on the number of entries allowed in catcaches,

Log Message:
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Remove the limit on the number of entries allowed in catcaches, and
remove the infrastructure needed to enforce the limit, ie, the global
LRU list of cache entries. On small-to-middling databases this wins
because maintaining the LRU list is a waste of time. On large databases
this wins because it's better to keep more cache entries (we assume
such users can afford to use some more per-backend memory than was
contemplated in the Berkeley-era catcache design). This provides a
noticeable improvement in the speed of psql \d on a 10000-table
database, though it doesn't make it instantaneous.

While at it, use per-catcache settings for the number of hash buckets
per catcache, rather than the former one-size-fits-all value. It's a
bit silly to be using the same number of hash buckets for, eg, pg_am
and pg_attribute. The specific values I used might need some tuning,
but they seem to be in the right ballpark based on CATCACHE_STATS
results from the standard regression tests.

Modified Files:
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pgsql/src/backend/utils/cache:
catcache.c (r1.128 -> r1.129)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/catcache.c.diff?r1=1.128&r2=1.129)
syscache.c (r1.103 -> r1.104)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/syscache.c.diff?r1=1.103&r2=1.104)
pgsql/src/include/utils:
catcache.h (r1.58 -> r1.59)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/catcache.h.diff?r1=1.58&r2=1.59)