Fix for #1672

[paulbaumgart]

I was experiencing the same issue as described here: https://github.com/isaacs/npm/issues/1672

I tracked it down to a problem with chmod when passing in a numerical group id. Probably a vmware fusion bug.

Do you know if anything else will ever generate an er.code of UNKNOWN? If not, this is a safe patch to apply. If yes, I will try and figure out a better condition to check.

[isaacs]

The error code of "UNKNOWN" simply means that it's an error number that libuv doesn't know about. (Since windows and unix have such widely different error codes, we use libuv to bridge the gap, rather than translating error numbers directly.)

However, since the chmod is arguably an optional thing in this case, I'd say it's probably fine to ignore. I'm not sure whether it's better to do here, though, or in graceful-fs, kind of like how chown is handed (by ignoring it if you're not root.)

[paulbaumgart]

Oh, yeah, graceful-fs looks like a much cleaner place to put this. I opened a pull request there: isaacs/node-graceful-fs#5