Disable xdebug.max_nesting_level in __init_script__.php

Summary:

• See T1192.
• Do all the environment stuff before including code.
• Do output buffer stuff first since it will completely silence any errors in the other things.

Test Plan:

• Set xdebug.max_nesting_level to 5, ran "arc". After this change, no error.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1192

Differential Revision: https://secure.phabricator.com/D2414