[LyX/master] Add a comment and FIXME that lualatex can make DVI

[Scott Kostyshak]

commit 2db62cf5d548ac6307134496b1fa8fbb8422327d
Author: Scott Kostyshak <skost...@lyx.org>
Date:   Sat Jun 11 17:05:28 2016 -0400

    Add a comment and FIXME that lualatex can make DVI
    
    The command 'lualatex' can produce a DVI with the option
    --output-format=dvi
    It is best to keep things as is because it is better to guess a PDF
    than to guess a DVI (we do not use that feature of the 'lualatex'
    command internally; we use 'dvilualatex' instead). However, we
    should ideally get this information in a more robust way.
    
    Thanks to Günter for pointing this out.

diff --git a/src/LaTeX.cpp b/src/LaTeX.cpp
index e8a6f9f..cfa6e1d 100644
--- a/src/LaTeX.cpp
+++ b/src/LaTeX.cpp
@@ -97,6 +97,12 @@ LaTeX::LaTeX(string const & latex, OutputParams const & rp,
        : cmd(latex), file(f), path(p), lpath(lp), runparams(rp), biber(false)
 {
        num_errors = 0;
+       // lualatex can still produce a DVI with --output-format=dvi. However,
+       // we do not use that internally (we use the "dvilualatex" command) so
+       // it would only happen from a custom converter. Thus, it is better to
+       // guess that lualatex produces a PDF than to guess a DVI.
+       // FIXME we should base the extension on the output format, which we 
should
+       // get in a robust way, e.g. from the converter.
        if (prefixIs(cmd, "pdf") || prefixIs(cmd, "lualatex") || prefixIs(cmd, 
"xelatex")) {
                depfile = FileName(file.absFileName() + ".dep-pdf");
                output_file =