Fix LaTeX error message printing

The original way of printing LaTeX error messages in batch mode was to redirect them to the standard output file, i.e. /dev/stdout.

However, this approach appreared to not be fully portable, so as writing to /dev/tty.

As proposed by Antoine Jego, acquiring the output filename dynamically, i.e. using the tty, could improve the portability. Unfortunately, since the Elisp interpreter is not executing the tty command within a TTY, it does not work in our case.

I propose a higher-level solution. The idea is to get the error message from the corresponding buffer and print it out using the message Elisp function. This way, the interpreter shall take care of finding the correct output file to write in.