Bump phpunit XSD version to 5.2

Some attributes being used in the phpunit configuration files, namely
failOnRisky and failOnWarning were introduced in phpunit 5.2.0. The
Composer configuration shows that tests should run with old versions of
phpunit, but phpunit only validates the configuration against the XSD
since phpunit 7.2.0.
These changes can be tested as follows:

wget http://schema.phpunit.de/5.2/phpunit.xsd
xargs xmllint --schema phpunit.xsd  1>/dev/null
find src -name phpunit.xml.dist| xargs xmllint --schema phpunit.xsd  1>/dev/null

See 7e06a82806
See 46e3745a03/composer.json (L98)

ClassCollectionLoader.php

@@ -53,7 +53,7 @@ class ClassCollectionLoader
             $classes = array_diff($classes, $declared);
 
             // the cache is different depending on which classes are already declared
-            $name = $name.'-'.substr(hash('sha256', implode('|', $classes)), 0, 5);
+            $name .= '-'.substr(hash('sha256', implode('|', $classes)), 0, 5);
         }
 
         $classes = array_unique($classes);

Tests/ApcClassLoaderTest.php

@@ -19,7 +19,7 @@ class ApcClassLoaderTest extends TestCase
 {
     protected function setUp()
     {
-        if (!(ini_get('apc.enabled') && ini_get('apc.enable_cli'))) {
+        if (!(filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) && filter_var(ini_get('apc.enable_cli'), FILTER_VALIDATE_BOOLEAN))) {
             $this->markTestSkipped('The apc extension is not enabled.');
         } else {
             apcu_clear_cache();
@@ -28,7 +28,7 @@ class ApcClassLoaderTest extends TestCase
 
     protected function tearDown()
     {
-        if (ini_get('apc.enabled') && ini_get('apc.enable_cli')) {
+        if (filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) && filter_var(ini_get('apc.enable_cli'), FILTER_VALIDATE_BOOLEAN)) {
             apcu_clear_cache();
         }
     }

Tests/LegacyApcUniversalClassLoaderTest.php

@@ -21,7 +21,7 @@ class LegacyApcUniversalClassLoaderTest extends TestCase
 {
     protected function setUp()
     {
-        if (ini_get('apc.enabled') && ini_get('apc.enable_cli')) {
+        if (filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) && filter_var(ini_get('apc.enable_cli'), FILTER_VALIDATE_BOOLEAN)) {
             apcu_clear_cache();
         } else {
             $this->markTestSkipped('APC is not enabled.');
@@ -30,7 +30,7 @@ class LegacyApcUniversalClassLoaderTest extends TestCase
 
     protected function tearDown()
     {
-        if (ini_get('apc.enabled') && ini_get('apc.enable_cli')) {
+        if (filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN) && filter_var(ini_get('apc.enable_cli'), FILTER_VALIDATE_BOOLEAN)) {
             apcu_clear_cache();
         }
     }

phpunit.xml.dist

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.1/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/5.2/phpunit.xsd"
          backupGlobals="false"
          colors="true"
          bootstrap="vendor/autoload.php"