Add ability to launch a site on a subdir right away on creation

[oskosk]

Notes:

mkdir subdir
mv * subdir
mv .htaccess subdir

wp search-replace ‘oldsite’ ‘newsite/subdir’

define('WP_SITEURL', SP_REQUEST_URL .);
define('WP_HOME', SP_REQUEST_URL);

fix .htaccess to add rewrites

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /subdir
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /subdir/index.php [L]
</IfModule>

# END WordPress