pgbouncer - pgbouncer: require libevent >= 1.3b

Log Message:
-----------
require libevent >= 1.3b

Modified Files:
--------------
pgbouncer:
NEWS (r1.20 -> r1.21)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/NEWS.diff?r1=1.20&r2=1.21)
README (r1.2 -> r1.3)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/README.diff?r1=1.2&r2=1.3)
configure.ac (r1.36 -> r1.37)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/configure.ac.diff?r1=1.36&r2=1.37)