We want to set migrated content file in the File module as a main file.
Main files are files with sortorder set to 1. Therefore the file manager
must provide a way to set the sortorder property of the new file record.
The second change allowing filepaths not ending with slash is a helper
as we can easily use dirname() as a value (see the usage in the next
commits). Not providing the dirname() was a bug as the reference to a
file in the HTML text did not respect the migrated file path.
The embedded files are now converted into the proper file area on the
conversion. The previous usage of $CFG->wwwroot/file.php was wrong for two
reasons: (1) the moodle.xml does not (should not) contain these links but
$@FILEPHP@$ placeholder and (2) even if it did, we could not compare to
our wwwroot but to the original wwwroot.
Also fixed the actual list of fields being written into page.xml - the
previous version included legacy fields (like type, reference and
friends).
