[2.3] If Loader is not immutable, override Apache env vars

[GabeMedrash]

This PR fixes #39.

I have not written additional tests due to the added complexity of introducing Apache as a dependency of the test suite, but I would be happy to provide some if you would like.

[GrahamCampbell]

Please follow PSR-2.

[GabeMedrash]

Thanks for the review--I ran phpcs --standard=PSR2 src and moved the body of the nested if within curly braces. The lint now runs clean. Let me know if there's something else you had in mind.

[GrahamCampbell]

Nearly there. Please get rid of the nested if too. ;)

[GabeMedrash]

Gotchya--think I got it this time!

[GrahamCampbell]

Thanks. Looks good to me. Ping @vlucas for approval.

[vlucas]

Looks good to me. The only question I have is that we can probably only check if one of the apache get/set functions exist, because if the module is enabled, both of them will always exist. It's more of a minor thing though, and not a reason to hold up this PR.

[GabeMedrash]

@vlucas Thanks, that makes a lot of sense. Will modify now.

[vlucas]

Thanks 👍