Tweak for r29770 (yes, some months after it):

Tweak for r29770 (yes, some months after it):
If the wiki is read only mode, don't show a "database locked" error if previewing or showing diff, but rather the "normal" action with a warning that the database is currently locked. If the user is trying to save the page, he'll see the preview page instead. Currently, if you are saving or previewing a page while the database is locked, you'll see the "database locked" error with the current text (or no text at all if the page doesn't exist), not your text, this might be confusing.

Also added the reason of the lock to the readonlywarning message.