The trunk version of EditPage::editForm is currently a roughly 500-line function
that builds the Edit page in all its various manifestations. Its large size and
number of variations (preview, diff, new article, edit conflict, etc.) make it
difficult to understand and improve. The function should be refactored so that
the bulk of its code is handed off to auxiliary functions, and what remains is
clear enough to follow the logic in building the edit form.