pgbouncer - pgbouncer: big pkt code reorg.

Log Message:
-----------
big pkt code reorg.

in old code the 'pkt' contained whateved data was available
from SBuf, which made sanity checks complex.

this patch creates wrapper structure for passing current packet
info around.

Modified Files:
--------------
    pgbouncer/src:
        admin.c (r1.16 -> r1.17)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/admin.c.diff?r1=1.16&r2=1.17)
        admin.h (r1.2 -> r1.3)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/admin.h.diff?r1=1.2&r2=1.3)
        bouncer.h (r1.12 -> r1.13)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/bouncer.h.diff?r1=1.12&r2=1.13)
        client.c (r1.14 -> r1.15)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/client.c.diff?r1=1.14&r2=1.15)
        mbuf.h (r1.2 -> r1.3)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/mbuf.h.diff?r1=1.2&r2=1.3)
        proto.c (r1.8 -> r1.9)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/proto.c.diff?r1=1.8&r2=1.9)
        proto.h (r1.1.1.1 -> r1.2)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/proto.h.diff?r1=1.1.1.1&r2=1.2)
        server.c (r1.12 -> r1.13)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/server.c.diff?r1=1.12&r2=1.13)
        takeover.c (r1.5 -> r1.6)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/takeover.c.diff?r1=1.5&r2=1.6)