pgbouncer - pgbouncer: fix signedness warnings in code

Log Message:
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fix signedness warnings in code

Modified Files:
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pgbouncer/src:
admin.c (r1.20 -> r1.21)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/admin.c.diff?r1=1.20&r2=1.21)
mbuf.h (r1.3 -> r1.4)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/mbuf.h.diff?r1=1.3&r2=1.4)
proto.c (r1.11 -> r1.12)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/proto.c.diff?r1=1.11&r2=1.12)
varcache.c (r1.6 -> r1.7)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/varcache.c.diff?r1=1.6&r2=1.7)