per Dmitry Samersoff:

If the mercurial wrapper uses:

#!/usr/bin/env python

this is confusing to hgforest.sh

I am testing the sed expression with:

#!/usr/bin/python
#!/usr/bin/python -B -E
#! /usr/bin/python
#! /usr/bin/python -B -E
#!/usr/bin/env python
#!/usr/bin/env python -B -E
#! /usr/bin/env python
#! /usr/bin/env python -B -E

(more variations are, of course, welcome).