#4773 Make warnings consistent

[David Scherfgen]

Warning messages in Maxima are inconsistent:

• Some start with "WARNING", some with "Warning", some with "warning".
• Some have an extra newline at the end, some don't.
• Some are printed to stderr, some to stdout.

Ideally, warnings should all be printed with the same function. There is mwarning, which unfortunately only concatenates its argument. It would be nicer if it worked like mtell, forwarding to mformat.

Possible solutions coming to my mind:

• Hack the existing mwarning: If its first argument looks like a format string with ~ -> use mformat. May cause false positives!
• Define a new function like mwarn or mtellwarn.
• Add a keyword argument :warning to mtell.