MDL-51179 Atto: Extend autosave fix to cover text changes

Added new functions to editor api - set/get_text so the
original form text can be determined from an editor.

When calling use_editor() you should first call set_text() with
the text that will be inserted in the form element.

There is also a new scheduled task for cleaning Atto autosave drafts.

lib/deprecatedlib.php

@@ -1205,6 +1205,7 @@ function print_textarea($unused, $rows, $cols, $width, $height, $name, $value=''
 
     editors_head_setup();
     $editor = editors_get_preferred_editor(FORMAT_HTML);
+    $editor->set_text($value);
     $editor->use_editor($id, array('legacy'=>true));
 
     $str .= "\n".'<textarea class="form-textarea" id="'. $id .'" name="'. $name .'" rows="'. $rows .'" cols="'. $cols .'" spellcheck="true">'."\n";