OptionFile says permission denied when file does not exist

[Peter]

I have an OptionOutFile that is created as

OptionOutFile out_pos(cmd, "p,positive", "output positive", true);

during validation I caught an exception with this message

cannot create file `result/imap/20090717/histogram.pos.txt.20': Permission denied

checking my tree I found that result/imap does not exist and I think the error message could say that instead. See, e.g., the error message when trying to 'cp SRC TGT' and the TGT directory does not exist.

Docs of FileUtil says that errno is set in FileUtil::permissions, so couldn't we use strerror to get an appropriate string?

[Peter]

(In [2049]) using strerror in error msg from OptionFile? (fixes #559)