cleanup dirstate->store_item
more head/wd separation
minor fixes
more head/md splitting.
dirstate->repos: convenience function
make scan_repo a method of dirstate
determine repo prefix automatically for dirstate items
further splitting. First find all changes, then walk the git tree to
find unchanged siblings.
get rid of @repos
reorder code, start reimplementing apply-commit mode
some placeholder code for a repository object
no default date