multisite install_blog() should honor UPLOADBLOGSDIR

[ktdreyer]

Currently (3.0.4), wp-includes/ms-functions.php's install_blog() just sets 'upload_path' to a hard-coded relative path.

update_option('upload_path', "wp-content/blogs.dir/" . $blog_id . "/files");

Grep for UPLOADBLOGSDIR and you'll see that it is only used in wp-includes/ms-default-constants.php, where the constant is initially set. wp-includes/ms-functions.php should use it, at least.

[ocean90]

#15383