Mark slow tests

Each of these tests took more than ten seconds on a recent AppVeyor CI
run; that appears to qualify them to be marked as slow tests.

Author: cmb69

Zend/tests/bug79514.phpt

@@ -1,5 +1,9 @@
 --TEST--
 Bug #79514 (Memory leaks while including unexistent file)
+--SKIPIF--
+<?php
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
+?>
 --FILE--
 <?php
 $mem1 = memory_get_usage(true);

ext/mysqli/tests/bug79375.phpt

@@ -2,6 +2,7 @@
 Bug #79375: mysqli_store_result does not report error from lock wait timeout
 --SKIPIF--
 <?php
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
 require_once('skipif.inc');
 require_once('skipifconnectfailure.inc');
 if (!defined('MYSQLI_STORE_RESULT_COPY_DATA')) die('skip requires mysqlnd');

ext/mysqli/tests/mysqli_fetch_array_large.phpt

@@ -2,6 +2,7 @@
 mysqli_fetch_array() - large packages (to test compression)
 --SKIPIF--
 <?php
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
 require_once('skipif.inc');
 require_once('skipifconnectfailure.inc');
 ?>

ext/openssl/tests/openssl_free_key.phpt

@@ -4,6 +4,7 @@ void openssl_free_key ( resource $key_identifier );
 marcosptf - <marcosptf@yahoo.com.br> - @phpsp - sao paulo - br
 --SKIPIF--
 <?php
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
 if (!extension_loaded("openssl"))
     die("skip");
 if (!@openssl_pkey_new())

ext/standard/tests/file/005_variation-win32.phpt

@@ -5,6 +5,7 @@ Test fileatime(), filemtime(), filectime() & touch() functions : usage variation
 if (substr(PHP_OS, 0, 3) != 'WIN') {
     die('skip Windows-only test');
 }
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
 ?>
 --FILE--
 <?php