This patch makes the xattr functions skip devices and special files,
because OS X returns the wrong errno when getting/setting xattrs on
them (it returns EPERM instead of ENOTSUP).

To use this patch, run these commands for a successful build:

    patch -p1 <patches/osx-xattr-nodev.diff
    ./configure                         (optional if already run)
    make

based-on: a01e3b490eb36ccf9e704840e1b6683dab867550