Support for rsyslog high precision timestamps

Per the discussion in #1023755, this adds support for rsyslog high-precision timestamp format to all logcheck rules.

It also avoids warnings from latest grep about stray backslashes ('grep: warning: stray \ before -' etc) -- this last part is the same as merge request !14 (merged) on which these commits build.

(it is based on the last upload ie 1.3.24 - it should be very easy to rebase or merge against the current HEAD to include the changes in git - but i wasnt sure if all of those were really 'ready' for inclusion in an upload or not)