convert: handle past or foreign partial svn copies
Subversion allows revisions to be composed of subparts coming from revisions
before the parent or from other part of the repository. There is no simple
representation for these now, keep the changes but do not track their origins.
% 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 *******