Add fs package

Add diff comparison with support for double walking
two trees for comparison or single walking a diff
tree. Single walking requires further implementation
for specific mount types.

Add directory copy function which is intended to provide
fastest possible local copy of file system directories
without hardlinking.

Add test package to make creating filesystems for
test easy and comparisons deep and informative.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

fs/hardlink_unix.go

@@ -0,0 +1,33 @@
+// +build !windows
+
+package fs
+
+import (
+	"errors"
+	"os"
+	"syscall"
+)
+
+func getHardLink(name string, fi os.FileInfo, inodes map[uint64]string) (string, error) {
+	if fi.IsDir() {
+		return "", nil
+	}
+
+	s, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return "", errors.New("unsupported stat type")
+	}
+
+	// If inode is not hardlinked, no reason to lookup or save inode
+	if s.Nlink == 1 {
+		return "", nil
+	}
+
+	inode := uint64(s.Ino)
+
+	path, ok := inodes[inode]
+	if !ok {
+		inodes[inode] = name
+	}
+	return path, nil
+}