Warn in GUI when mixing Title and InTitle layouts
Since we process layouts sequentially, we export LaTeX code for the
title once we arrive to a layout that has InTitle false. If the
document then later has a layout with InTitle true, we do not
(currently) go back to add it to the title and just output it
in-place. We previously warned with LYXERR0, but since this can
cause missing or unexpected output we now warn in the GUI.
For more information, see the following lyx-devel thread:
https://www.mail-archive.com/search?l=mid&q=
a65ae226-d3bd-8fc5-a93b-
7bb23f1cda82%40lyx.org