Changed the behaviour of getenv() for env values in phpunit 4.8.33

[ezimuel]

I just discovered this merging a PR for zendframework/zend-http.
If we have some env values in phpunit.xml, for instance:

<env name="TESTS_BASEURI" value="false" />

and we get this value using getenv('TESTS_BASEURI') in a test case, we will get the string "false" in 4.8.33 and an empty string in 4.8.32.
This is a potential BC break for many unit tests.

[sebastianbergmann]

This is due to #2331.

[ezimuel]

@sebastianbergmann but this a BC break, right?

[ezimuel]

@sebastianbergmann thanks for 4.8.34 release!