Because some extensions add functions that generate cached images, deleteFormattedImages()
needs to find all the method names by passing true to allMethodNames().
Apply preg_quote to each generator name and to $this->Name so that their use in a
regular expression will not cause run-time errors.
Provided fixture and test.
ENHANCEMENT New FileNameFilter class for a more customisable way to influence filename filtering in Upload->load(), Folder->addUploadToFolder() or Image->loadUploadedImage()
