Bugs in Batch Create

Hi,

thanks for the helpfull 'Batch Create' plugin! I think I found two bugs:

1) There is a SQL statement that uses "FROM wp_users" instead of "FROM $wpdb->users"

2) In the batch_create_process_queue function, "$base = $current_site->path" probably would be better than the current "$base = '\'"

3) It's not a bug but a bit problematic: empty lines in the CSV file (and files tend to have one empty paragraph at the end) will create a user without name/pass. So I added a check for empty lines when reading the content of the file.