On Linux use the C library's xattr support before trying libattr

Hi Richard,

For Linux, I've updated the build to use the C library's xattr support from <sys/xattr.h> if it's there, and fall back on libattr if it's not.

I also migrated the .cvsignore to .gitignore and updated the bundled Devel::Checklib.

Sorry it's all in one pull request, I forgot I couldn't choose which commits to pull.

Hope it's all okay, let me know if otherwise!

Thanks