tests/test-churn.out

store: simplify walking

- fold in main walking function
- eliminate recursion (especially recursive yielding!)
- eliminate default args

% create test repository
adding a
adding b
adding c
% churn all
user3      3 ***************************************************************
user2      2 ******************************************
user1      1 *********************
% churn up to rev 1
user2      2 ***************************************************************
user1      1 *******************************
% churn with aliases
alias3      3 **************************************************************
user2       2 *****************************************
alias1      1 ********************
% churn with column specifier
user3      3 ***********************
user2      2 ***************
user1      1 *******