Only parse the stdout from direnv export json

[stribb]

Then, put stderr into *direnv*.

Side effect: exit code now only affects the warning message.

Tested:

Happy path: I ran (direnv--export "/Users/andstrib/somedir") and it returns a list of environment key/value cons pairs. *direnv* contained the output and a line from stderr.

Unhappy path: Then I changed the function to run direnv export this-does-not-work and re-ran it. It didn't parse the error message, but did write to *Messages* and *direnv*.

[wbolster]

done in b334a4a:

Improve handling of direnv output (#42)

Only parse JSON from direnv stdout. Output on stderr still goes into the direnv buffer, but will never be parsed.

When a problem occurs, emit a warning, since a normal message will not be visible. An example scenario is switching from a functional direnv directory to a broken one (e.g. unapproved .envrc). The unloading of the first directory will be shown as a summary message, and the message emitted about the problem will be overwritten and hence will go unnoticed. Instead, use (warn ...) which will pop up a window with more details instead.

Fixes #41.

[wbolster]

thanks @stribb!