Please make the 'env updates os.environ only' feature optional

[Margarethe Meier]

Hi,

we plan to use your library in out application, but we have one major concern. For our subprocesses we need to clean os.environ and therefore pass a fixed env variable to the subprocesses. So if you could provide a flag like ‘replace_env’ this would be great.

[Vinay Sajip]

Fixes #47: Added replace_env keyword argument to allow overriding child process environment completely.

→ <<cset c1f7501419b0>>

[Vinay Sajip]

Please try this version to ensure that it meets your needs, before I make a new release.