String and ByteString implementations have desynchronized

[ezyang]

I've been Backpack'ifying unix on the suggestion of @hvr, and I have realized that the String and ByteString implementations have desynchronized in a few cases. I'm still working my way through the modules but here are the ones I've noticed:

System.Posix.Env

• ByteString does not implement/export setEnvironment
• ByteString: unsetEnv name = putEnv (name ++ "=") Pretty sure this is a type error
• ByteString: putEnv uses useAsCString to allocate the string passed to putenv, but String has a comment indicating we must not free the string after putenv according to SUSv2

Actually, amazingly enough, I checked the rest of the implementations and this was the only desynchronization.

[hasufell]

The third point causes a serious bug:

With String:

Prelude> import System.Posix.Env
Prelude System.Posix.Env> putEnv "foo=bar"
Prelude System.Posix.Env> getEnv "foo"
Just "bar"
Prelude System.Posix.Env> getEnv "foo"
Just "bar"

With ByteString:

Prelude> import System.Posix.Env.ByteString
Prelude System.Posix.Env.ByteString> :set -XOverloadedStrings
Prelude System.Posix.Env.ByteString> putEnv "foo=bar"
Prelude System.Posix.Env.ByteString> getEnv "foo"
Just "bar"
Prelude System.Posix.Env.ByteString> getEnv "foo"
Nothing