Fix missing values in unittest harness

1. Symptom: global $lang is empty for all unittests.

Cause: use of require_once() in init_lang() after clearing the $lang global.  

2. Symptom: when called from CLI, some $_SERVER values are missing.

Cause: although $_SERVER is mocked for each test, the call to inc/init.php occurs in bootstrap.php when several $_SERVER values maybe missing.