[php] Fix widespread use of bare strings in testsuite

These generate warnings with PHP 7.3, which will become errors in a
future version.

Examples/test-suite/php/director_extend_runme.php

@@ -4,9 +4,9 @@ require "tests.php";
 require "director_extend.php";
 
 // No new functions
-check::functions(array(spobject_getfoobar,spobject_dummy,spobject_exceptionmethod));
+check::functions(array('spobject_getfoobar','spobject_dummy','spobject_exceptionmethod'));
 // No new classes
-check::classes(array(SpObject));
+check::classes(array('SpObject'));
 // now new vars
 check::globals(array());