[PULL REQUEST] Add support for Apache alias

I cant really do a pull request with SVN but here is some modifications.

Issue:
I got a website at in /var/www/website that is executing when ever I access http://www.domain.com/. I got a wordpress blog in /var/www/wordpress. I’ve configured Apache with an alias like

Alias /site "/var/www/wordpress"
<Directory "/var/www/wordpress">
      AllowOverride All
      Allow from All
</Directory>

There are two problems with the plugin when running this setup.
#1 w3_get_document_root() and w3_get_home_root() are returning blank strings
#2 RewriteBase is misconfigured for the minify/.htaccess

Solution:
I made some changes to the functions named in #1.

function w3_get_document_root() {
    static $document_root = null;
    $len = strlen($_SERVER['PHP_SELF']);
    $split = $len/2;

    if ($document_root === null) {
        if (!empty($_SERVER['SCRIPT_FILENAME']) && $_SERVER['SCRIPT_FILENAME'] == $_SERVER['PHP_SELF']) {
            $document_root = w3_get_site_root();
        } elseif (!empty($_SERVER['DOCUMENT_ROOT'])) {
            //get the script path without the HOME
            $phpSelf=str_replace(w3_get_home_path(), '',w3_path($_SERVER['PHP_SELF']));

            $document_root = substr(w3_path($_SERVER['SCRIPT_FILENAME']), 0, -strlen($phpSelf));
        } elseif (!empty($_SERVER['PATH_TRANSLATED'])) {
            $document_root = substr(w3_path($_SERVER['PATH_TRANSLATED']), 0, -strlen(w3_path($_SERVER['PHP_SELF'])));
        } elseif (!empty($_SERVER['DOCUMENT_ROOT'])) {
            $document_root = w3_path($_SERVER['DOCUMENT_ROOT']);
        } else {
            $document_root = w3_get_site_root();
        }

        $document_root = realpath($document_root);
        $document_root = w3_path($document_root);
    }

    return $document_root;
}

function w3_get_home_root() {
    if (w3_is_network()) {
        $path = w3_get_base_path();
    } else {
        $path = w3_get_home_path();
    }

    $root = w3_get_document_root();
    $home_root = $root . $path;
    $home_root = realpath($home_root);
    if($home_root === false){
        $home_root=$root;
    }
    $home_root = w3_path($home_root);

    return $home_root;
}

To address the problem in #2 if rewrote the rules_core_generate_apache() function.

function rules_core_generate_apache($config) {
        $is_network = w3_is_network();

        $base_path = w3_get_base_path();
        $home_path = w3_get_home_path();
        $rewrite_base = ($is_network ? $base_path : $home_path);
        $rewrite_base=rtrim($rewrite_base,'/');

        $cache_dir = w3_filename_to_uri(W3TC_CACHE_MINIFY_DIR);
        $minify_filename = w3_make_relative_path(W3TC_DIR . '/pub/minify.php',
            W3TC_CACHE_MINIFY_DIR);

        $engine = $config->get_string('minify.engine');
        $browsercache = $config->get_boolean('browsercache.enabled');
        $compression = ($browsercache && $config->get_boolean('browsercache.cssjs.compression'));

        $rules = '';
        $rules .= W3TC_MARKER_BEGIN_MINIFY_CORE . "\n";
        $rules .= "<IfModule mod_rewrite.c>\n";
        $rules .= "    RewriteEngine On\n";
        $rules .= "    RewriteBase " . $rewrite_base.$cache_dir . "/\n";
        $rules .= "    RewriteRule /w3tc_r
/* some more code.. */

Disclaimer:
This pull request is not ready to merge (since public unittests do not exist). I have not tried this solution in any other server configuration.

http://wordpress.org/plugins/w3-total-cache/