Fix PHP 5.2 build failure

lcfirst() isn't defined on PHP 5.2, so I added a fallback function, which
is defined in the bootstrap.php. Not sure whether that's the right place
to put it.

doc/1_Usage_of_basic_components.markdown

@@ -14,14 +14,6 @@ The library needs to register a class autoloader; you can do this either by incl
 require 'path/to/PHP-Parser/lib/bootstrap.php';
 ```
 
-Or by manually registering the loader:
-
-```php
-<?php
-require 'path/to/PHP-Parser/lib/PHPParser/Autoloader.php';
-PHPParser_Autoloader::register();
-```
-
 Parsing
 -------
 

lib/bootstrap.php

@@ -1,4 +1,14 @@
 <?php
 
 require dirname(__FILE__) . '/PHPParser/Autoloader.php';
-PHPParser_Autoloader::register();
+PHPParser_Autoloader::register();
+
+/*
+ * lcfirst() was added in PHP 5.3, so we have to emulate it for PHP 5.3.
+ */
+if (!function_exists('lcfirst')) {
+    function lcfirst($string) {
+        $string[0] = strtolower($string[0]);
+        return $string;
+    }
+}