pgbouncer - pgbouncer: Dont let logging change errno.

Log Message:
-----------
Dont let logging change errno.

With badly configured logging and higher logging levels, the code can
see wrong errno from syscalls. So always retore original errno when logging.

Modified Files:
--------------
pgbouncer/src:
util.c (r1.33 -> r1.34)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbouncer/pgbouncer/src/util.c?r1=1.33&r2=1.34)