dummyssh: make sure we don't inherit files descriptor to the children
This is one of the difference between python2 and python3 and could have been a
reason why test hang with python2 + chg. This does not seems to help the
hanging issue at all…
However, now that this is written lets reduce the difference between python2
and python3.
Differential Revision: https://phab.mercurial-scm.org/D11225
# rhg
This project provides a fastpath Rust implementation of the Mercurial (`hg`)
version control tool.