Unsuccessful imports are hard to detect

[Albert Brandl]

When the import mechanism encounters an error, the problem is reported in the
log area. But there is no indication that the imported tree is incomplete.
The import silently stops before the line that caused the error.

If someone does not watch the log area (or does not interpret the meaning of
the error message correctly), she might think that the import has worked.
This will result in the editing of an incomplete image of the original file,
which will cause problems in many cases.

I think it would be a good idea to show very clearly that the imported tree is
not complete. IMHO, a node that was not completely imported, should be marked
as incomplete, or the import of this node should be cancelled altogether.

If this is not possible, the error message should at least clearly indicate
that the resulting tree differs from the original file. This situation might even
call for a dialog box...

Best regards,

Albert