BF: failregex declared direct in jail was joined to single line, (specifying of multiple expressions was not possible);
feature request (gh-867): new options for jail introduced addfailregex/addignoreregex: extends regex specified in filter (opposite to failregex/ignoreregex that overwrites it);
test cases extended (now correct)
interpolation of config readers extended with `%(known/parameter)s`.
(means last known option with name `parameter`).
python 2.6 compatibility: preventing RuntimeError: dictionary changed size during iteration.
better and scalable solution for gh-867 (and gh-868), using only name convention like %(known/failregex)s to add custom expressions, so no interface changes in jail.conf are necessary (for example see test-known-interp in test cases);
Merge remote-tracking branch 'remotes/upstream/master' into sebres:addfailregex-gh-867
Merge pull request #868 from sebres/addfailregex-gh-867

"known/" prefix to allow reuse specs from prev files for addfailregex/addignoreregex (Close #867)