test-copies: improve description of the A+B case
This will make its role clearer.
Differential Revision: https://phab.mercurial-scm.org/D10037
test-copies: use intermediate variable some commit descriptions
Right now, everything mostly says "simple merge", we want to use something a bit
more descriptive. Before doing any changes, we do most of the churn. This helps
the next sets of changesets to be clearer.
Differential Revision: https://phab.mercurial-scm.org/D10036