Legacy Resource modules of the type Web page force the HTML format for
their content. The format stored in the reference field is valid only
for legacy resources of the type Plain text page. See page_20_migrate()
function.
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).
