Add intercept for writes to special OS applications
Robert Sprowson authored
When Filer_Visibility is set to hide special OS applications (!Boot, !Choices,
!Scrap, !Territory), monitor attempts to copy or move similarly named objects
into their place. Without this they would appear to vanish into a black hole.

If hidden, and an attempt to overwrite one of the special OS apps is made, the
operation is halted with a warning box similar to the read only warning. The
operation can be aborted entirely, that 1 clashing object can be skipped, or
the operation retried.

A new subreason to Message_FilerControlAction allows the visibility state to be
tracked "live", so while halted the user can go to !Configure and unhide them,
then click on Retry to complete the task.

Fix an issue that the error messages (ER0-ER3) were after a {DictTokens}
directive, but the messages are looked up using msgs_lookup() which doesn't use
MessageTrans and so doesn't understand tokenised strings.

Version 0.64. Tagged as 'FilerAct-0_64'
7db4bdec