bug#9319: Compilation fontification regression

[Chong Yidong]

Juri Linkov <juri@jurta.org> writes:

> * IBM jikes, Sparc Pascal, GCOV, Podchecker
>   - errors/warnings not highlighted,
>     so this looks like a bug.
>
> * ant
>   - warning highlighted with `error' face.  But maybe this change
>     is based on the user's request, I don't know.
>
> Other changes between 23.1 and 24.0 look like bug fixes
> that provide more correct fontification.
>
> 2. Sometimes errors/warnings are not fontified at all.
>    For instance,
>
>    C-x C-f etc/compilation.txt RET
>    C-s RET symbol: sun RET
>
> i.e. non-incremental search that goes directly to the given section,
> fontifies nothing.

Both problems were due to incorrect code in compilation-error-properties
causing it to signal an error for error definitions with nil filenames,
introduced when Stefan revamped compile.el.  I've committed a fix.