t(): Change the order of langcode and function_exists("locale") evaluation

In the t() function, translation can be sped up by making a trivial change to the order of evaluation of one `if` statement.

Line 1429 of bootstrap.inc has this:

elseif (function_exists('locale') && $options['langcode'] != 'en') {

String comparison is almost twice as fast as a function_exists() call. So a trivially easy change would reduce the time taken by t() for any case where the language is English, which I'd venture to guess is a substantial portion of the Drupal population.

I noticed that on the main site I am working on, t() is called over 6,000 times on an only moderately complex page. Making the switch makes a very real performance difference.

Example benchmarking script (`t_test.php`):

$langcode = "en";

function locale(){}

$start = microtime(TRUE);
for ($i = 0; $i < 600000; ++$i) $langcode != "en" && function_exists("locale");
$end = microtime(TRUE);

printf("strcmp first: %0.4f\n", $end - $start);

$start = microtime(TRUE);
for ($i = 0; $i < 600000; ++$i) function_exists("locale") && $langcode != "en";
$end = microtime(TRUE);

printf("function_exists first: %0.4f\n", $end - $start);

Sample output:

$ php ./t_test.php 
strcmp first: 0.2000
function_exists first: 0.9985

Environment:

$ uname -a
Linux dev-mbutcher 2.6.26-2-686 #1 SMP Mon Jun 21 05:58:44 UTC 2010 i686 GNU/Linux
$ php --version
PHP 5.2.6-1+lenny9 with Suhosin-Patch 0.9.6.2 (cli) (built: Aug  4 2010 03:25:57) 
Copyright (c) 1997-2008 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2008 Zend Technologies
    with eAccelerator v0.9.6.1, Copyright (c) 2004-2010 eAccelerator, by eAccelerator
    with Xdebug v2.0.3, Copyright (c) 2002-2007, by Derick Rethans