Backport xonsh fixes for env parsing
Backport xonsh fixes for env parsing

See https://github.com/xonsh/xonsh/commit/9047b7408c311dd0984ad00e73373c104ab1085a

Sourcing foreign shells now allow fully capture environment variables that
contain newlines as long as they also don't contain equal signs.

Cadair/jupyter_environment_kernels