pgbouncer - pgbouncer: document new -u/user= option

Log Message:
-----------
document new -u/user= option

Modified Files:
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pgbouncer/doc:
usage.txt (r1.3 -> r1.4)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/doc/usage.txt.diff?r1=1.3&r2=1.4)
config.txt (r1.5 -> r1.6)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/doc/config.txt.diff?r1=1.5&r2=1.6)