pgbouncer - pgbouncer: Remove concept of 'flushing' from code as bouncer

Log Message:
-----------
Remove concept of 'flushing' from code as bouncer does not actively buffer anything.

The flushing logic was remnant from the time when buffering was
pushed to kernel with MSG_MORE. Now it only complicates code.

Modified Files:
--------------
pgbouncer/src:
bouncer.h (r1.5 -> r1.6)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/bouncer.h.diff?r1=1.5&r2=1.6)
client.c (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/client.c.diff?r1=1.6&r2=1.7)
objects.c (r1.9 -> r1.10)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/objects.c.diff?r1=1.9&r2=1.10)
sbuf.c (r1.8 -> r1.9)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/sbuf.c.diff?r1=1.8&r2=1.9)
sbuf.h (r1.5 -> r1.6)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/sbuf.h.diff?r1=1.5&r2=1.6)
server.c (r1.7 -> r1.8)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/server.c.diff?r1=1.7&r2=1.8)
pgbouncer/test:
asynctest.c (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/test/asynctest.c.diff?r1=1.2&r2=1.3)