initial commit readdir tweak

[zedlopez]

Skips entries for which readdir returns errors. Both rv and errno are zero when readdir has truly run out of files, so it shouldn't infinitely loop. Probably advisable to test on Mac OS X and have someone test on Windows before merging.

[zedlopez]

addresses I7-2355

[zedlopez]

...not that I'd ever want to discourage multiplatform testing, but given that this change is to POSIX Platforms.w, testing on Windows seems less crucial than I originally suggested.

[ganelson]

This change works absolutely fine for me on MacOS, but I am a bit nervous about the possibility of a hang if the error reported by readdir is more of the "this directory is such a mess that I can't read it at all" kind. The Gnu documentation for readdir (though not other sources) actually says:

"To distinguish between an end-of-directory condition or an error, you must set errno to zero before calling readdir. To avoid entering an infinite loop, you should stop reading from the directory after the first error."

I wonder if the loop should only be continued if errno is a particular value associated with an error on a bad single file or link?

[zedlopez]

Yeah, I'd been having misgivings, too. I've committed a more discrete patch to my branch. OK, immediately after I commented that I didn't know why it hadn't updated the PR, I finally saw that it updated the PR.