Added Util class to help detect TTY properly. (#41)

src/Util/Tty.php

@@ -0,0 +1,23 @@
+<?php
+namespace Consolidation\SiteProcess\Util;
+
+use Symfony\Component\Process\Process;
+
+/**
+ * Wrapper for universal support of TTY-related functionality across versions of
+ * Symfony Process.
+ */
+class Tty
+{
+    /**
+     * In Symfony Process 4+, this is simply a wrapper for Process::isTtySupported().
+     * In lower versions, it mimics the same functionality.
+     */
+    public static function isTtySupported()
+    {
+        if (method_exists('\Symfony\Component\Process\Process', 'isTtySupported')) {
+            return Process::isTtySupported();
+        }
+        return (bool) @proc_open('echo 1 >/dev/null', array(array('file', '/dev/tty', 'r'), array('file', '/dev/tty', 'w'), array('file', '/dev/tty', 'w')), $pipes);
+    }
+}