ntp_: rewrite plugin to support IPv6

Closes Debian bug #558800 and Munin trac ticket #775
ntp_states: decrease timeouts so DNS queries don't cause node timeout
ntp_states: don't use this silly plugin loading method

Sometimes it causes differences in the way the module is loaded.
node.d/ntp_states: improve compatibility with older perls

The \R regex sequence was introduced in perl 5.10.0, so this did not
work on CentOS 5's perl 5.8.8. Using \s instead fixes this. Noticed by
leeclemens in pull request #80.