Any DDV (Dialog Data Validation) routine must appear immediately after the field it validates in order for the enforcement to work in real-time. If the DDV_ routine is not linked to the field, it will perform validation after-the-fact by displaying a dialog box and returning an error. This is an alternate way of handling validation, but in order for the dialog box not to generate an endless loop, it would be necessary to check the return value of every `UpdateData(TRUE)` call in the FRED codebase (or at least the first `UpdateData(TRUE)` in a pair of them) and then, if the return value is `FALSE`, doing an early return from the enclosing function.
Fixes#6427 as well as all similar cases in FRED.
FRED has an autosave feature but it wasn't invoked in too many places. This adds autosaving whenever a major dialog is closed, unless it was closed by hitting Cancel. NB: Autosave is not yet implemented in qtFRED.
Also, `addvariabledlg` incorrectly referred to `OnOk` instead of `OnOK` and `CMessageEditorDlg` incorrectly referred to `OnOK` instead of `OnOk`, so this fixes those and distinguishes `OnOk` by renaming it `OnButtonOk` to be consistent with the event editor and other dialogs.
Goober5000