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/fstest/compare.go

@@ -0,0 +1,37 @@
+package fstest
+
+import (
+	"github.com/pkg/errors"
+	"github.com/stevvooe/continuity"
+)
+
+// CheckDirectoryEqual compares two directory paths to make sure that
+// the content of the directories is the same.
+func CheckDirectoryEqual(d1, d2 string) error {
+	c1, err := continuity.NewContext(d1)
+	if err != nil {
+		return errors.Wrap(err, "failed to build context")
+	}
+
+	c2, err := continuity.NewContext(d2)
+	if err != nil {
+		return errors.Wrap(err, "failed to build context")
+	}
+
+	m1, err := continuity.BuildManifest(c1)
+	if err != nil {
+		return errors.Wrap(err, "failed to build manifest")
+	}
+
+	m2, err := continuity.BuildManifest(c2)
+	if err != nil {
+		return errors.Wrap(err, "failed to build manifest")
+	}
+
+	diff := diffResourceList(m1.Resources, m2.Resources)
+	if diff.HasDiff() {
+		return errors.Errorf("directory diff between %s and %s\n%s", d1, d2, diff.String())
+	}
+
+	return nil
+}