ShellSession.popen incorrectly processes Commands

[vient]

I think, or I am using it wrong.

Hi, so here https://github.com/tomerfiliba/plumbum/blob/v1.8.1/plumbum/machines/session.py#L280-L283 popen checks if cmd is BaseCommand, if so then calls formulate on it. After that it assumes that full_cmd is string but formulate returns list so popen crashes on full_cmd.strip() afterwards.

Should it be ' '.join(cmd.formulate(1)) on line 281?

[vient]

If I pass cmd as string by joining it then it works.
There is something strange in cases when ProcessExecutionError is raised though: command line is printed as a bunch of numbers which are ASCII codes of characters from original command. For example, abc becomes 97 98 99.