The QUESTION_CATEGORIES tag is optional in moodle.xml but the file
questions.xml is required by the moodle2 restore process. So here we
make sure that at least an empty file is created.
Kudos to Mark Nielsen for his initial work on this project. In his code,
Mark described the valuable logic of the conversion using a framework
mirroring plan/tasks/steps based architecture of the backup and restore.
My attempt to simplify it led to the current handlers-based
architecture.
Added write_xml() helper that writes the given tree-ish structure into
the current xml writer. Improved get_contextid() so that it can use
indices for searching data. Added set_stash() and get_stash() helper
methods.
This patch mainly adds support for dispatching path-start and path-end events,
defines API to access backup_ids_temp table. Some ideas emailed by Mark
after his first review of the code are incorporated already.
These are David's changes of Mark's code that replace the
plan/tasks/steps infrastructure with a bit simpler one. The changes will
be described in the next commit that will actually finish the
conversion.
TODO: refactor backup/converter/moodle1/stepslib.php into conversion
handlers.
* Several base_converter methods made protected when there was no obvious
reason why they should be public (subject of eventual change still).
* The conversion chain now constructed in advance before any converter
class is instantiated, using Dijkstra's algorithm.
