Comment 6 for bug 743003

Regarding the branch I attached, we can check the "errno" value directly if preferred, per your comments above, mvo. The specific check for the directory just seemed slightly more readable, but I'm sure it's slower (not that speed matters for this case).

If this fix seems ok, I'll wire it in for related bug 836172, bug 936917, bug 973293 and bug 975156.