implement incremental history index for file based repository
fixes #729
Merge pull request #766 from vladak/filehist_incr

implement incremenal history index for file based repository
do not list files for changesets when getting history for a file
fixes #768
Merge pull request #769 from vladak/parse_optimize

do not list files for changesets when getting history for a file
rework handling of latest revisions for list of repositories
fixes #771
create history data directories for renamed files before spawning the threads
fixes #775
missing space in exception message
Merge pull request #777 from vladak/finally_take2

rework handling of latest revisions for list of repositories
Merge pull request #776 from vladak/mkdir_races

create history data directories for renamed files before spawning the th...