pgsql: Modify local buffer management to request memory for local

Log Message:
-----------
Modify local buffer management to request memory for local buffers in blocks
of increasing size, instead of one at a time.  This reduces the memory
management overhead when num_temp_buffers is large: in the previous coding
we would actually waste 50% of the space used for temp buffers, because aset.c
would round the individual requests up to 16K.  Problem noted while studying
a performance issue reported by Steven Flatt.

Back-patch as far as 8.1 --- older versions used few enough local buffers
that the issue isn't significant for them.

Tags:
----
REL8_2_STABLE

Modified Files:
--------------
    pgsql/src/backend/storage/buffer:
        localbuf.c (r1.74 -> r1.74.2.1)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/localbuf.c.diff?r1=1.74&r2=1.74.2.1)