Disable Xsnmp preferences pane

Signed-off-by: Gregor Jasny <gjasny@googlemail.com>
Fix configure.ac version manipulation

Signed-off-by: Gregor Jasny <gjasny@googlemail.com>
Release Xsnmp 1.2.1

Signed-off-by: Gregor Jasny <gjasny@googlemail.com>