test-copies: add a case involving the `b` and a new `r` branch
That case involve a branch overwriting copies information from the other one.
It is similar to the `mBFm` / `mFBm` case except this case actual content merge
is involved too.
Differential Revision: https://phab.mercurial-scm.org/D10058
public attribute not declared in interfaces: badpeer.badattribute
public attribute not declared in interfaces: badpeer.badmethod