Description:
------------
libxml_set_external_entity_loader doesn't work with httpd built from source.

Example code from http://php.net/manual/en/function.libxml-set-external-entity-loader.php (Example 1)

Test script:
---------------
http://stackoverflow.com/questions/38683530/libxml-set-external-entity-loader-doesnt-work-in-httpd

Expected result:
----------------
string(10) "-//FOO/BAR"
string(25) "http://example.com/foobar"
array(4) {
  ["directory"]=>
  NULL
  ["intSubName"]=>
  NULL
  ["extSubURI"]=>
  NULL
  ["extSubSystem"]=>
  NULL
}
bool(true)

Actual result:
--------------
Warning: DOMDocument::validate(http://example.com/foobar): failed to open stream: HTTP request failed! HTTP/1.0 404 Not Found in /www/test.php on line 28

Warning: DOMDocument::validate(): I/O warning : failed to load external entity "http://example.com/foobar" in /www/test.php on line 28

Warning: DOMDocument::validate(): Could not load the external subset "http://example.com/foobar" in /www/test.php on line 28
bool(false)