remove old cruft and make Mercurial history parsing more strict so that it can detect format changes
fixes #743
Merge pull request #744 from vladak/mercurial_parsing

remove old cruft and make Mercurial history parsing more strict so that ...
human readable time format for duration of history index
fixes #745
Merge pull request #746 from vladak/histindex_time

human readable time format for duration of history index