Tests: PHP extension mounts.

test/php/list-extensions/index.php

@@ -0,0 +1,11 @@
+<?php
+
+function quote($str) {
+    return '"' . $str . '"';
+}
+
+header('Content-Type: application/json');
+
+print "[" . join(",", array_map('quote', get_loaded_extensions())) . "]";
+
+?>

test/php/list-extensions/php.ini

@@ -0,0 +1 @@
+extension=json.so