Explain to Emacs how Why3 locate errors.
This fixes expectations 1 and 2 of issue #706. Expectation 3 (accented characters) is still broken. This puts Emacs on par with Why3's IDE.
This fixes expectations 1 and 2 of issue #706. Expectation 3 (accented characters) is still broken. This puts Emacs on par with Why3's IDE.