subrepo: clone of git sub-repository creates incorrect git branch (issue3870)
Mercurial handles git subrepos by incorrect way.
If the mercurial repo has a git sub-repo and somebody started
a new branch in the subrepo and push it into git, the next one
who will clone the whole repo will get incorrect branch name in the git
subrepo.
% creating repo
% add and commit
C test.py
% change
M test.py