Co-authored-by: Sujith Haridasan <sujith@moodle.com>

dirname() is a slow function compared with __DIR__ and using
'/../'.  Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code.  This allows those required includes to perform as
best as possible in this situation.

This reverts commit ab7632b7.

* Added a comment for the BOOK_NUM_* defines.
* Fixed broken redirects in tool/importhtml/index.php
* Fixed typo in book_preload_chapters [subchpaters => subchapters]
* Fixed copy paste docblock error in tool/print/locallib.php
* Removed the .gitignore file as Eloy had previously mentioned that.