bugfix: potential segfault on rsyslog termination in imudp

closes: http://bugzilla.adiscon.com/show_bug.cgi?id=456
imtcp: fix typo in config parameter name
imtcp: permit parameter name with typo for backward compatibility
typo fix ("listner" vs. "listener")
doc: update ChangeLog
build: fix issues on FreeBSD

The last fix was incomplete. Thanks to Christiano for testing
and suggestions.