fix the save dialogs in the script editor

[madewokherd]

Imported from https://sourceforge.net/apps/mantisbt/urk/view.php?id=12

The save as, save confirmation, and overwrite confirmation dialogs in the script editor are a weird combination of modal and non-modal. Weird things happen when they're open.

These dialogs should be modal ONLY for the window that created them. I.e. a script window asking you to save shouldn't prevent you from sending a message to your friends in #urk.