Please define PQ_BUFFER_SIZE in interfaces/libpq/fe-misc.c

Hi,

I am accelerating the transfer of resultset
from backend to client using the zlib library.
While coding, I was surprised that
magic number 8192 (which is defined as PQ_BUFFER_SIZE in
backend/libpq/pqcomm.c) are written into the code
in interfaces/libpq/fe-misc.

I thought the magic number should be eliminated.
So I defined the magic number 8192 as PQ_BUFFER_SIZE in fe-misc.c.
The result is attached to this mail.
# it is just a slight modification

I am very happy if you accept my proposition.

Best regards,

-- Hideyuki Kawashima
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Hideyuki KAWASHIMA <kawasima(at)ayu(dot)ics(dot)keio(dot)ac(dot)jp> Ph.D.
Research Associate, Keio University