plugin/file: Rename do to walk and cleanup and document (#2987)

* plugin/file: Rename do to walk, cleanup and document

* This renames Do to Walk to be more inline with Go standards. Also make
  it return an error instead of a bool.
  Also give give walk access to rrs. Alternatively e.m could be
  exported, but just access the map of rrs should work as well. Another
  alternative would be adding a whole bunch of helper functions, but
  those need grab and return the data. Just having access to the rrs
  should be easiest for most Walks.
* It adds Type and TypeForWildcard to show the different functions
* *Removes* the identical RR check when inserting; this was only done
  for A, AAAA and MX and not finished; removed under the mantra garbage
  in garbage out.
* Reuses Types to return all the types in an *tree.Elem

Signed-off-by: Miek Gieben <miek@miek.nl>

* better comments

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/file/tree/all.go

@@ -1,6 +1,6 @@
 package tree
 
-// All traverses tree and returns all elements
+// All traverses tree and returns all elements.
 func (t *Tree) All() []*Elem {
 	if t.Root == nil {
 		return nil
@@ -19,30 +19,3 @@ func (n *Node) all(found []*Elem) []*Elem {
 	}
 	return found
 }
-
-// Do performs fn on all values stored in the tree. A boolean is returned indicating whether the
-// Do traversal was interrupted by an Operation returning true. If fn alters stored values' sort
-// relationships, future tree operation behaviors are undefined.
-func (t *Tree) Do(fn func(e *Elem) bool) bool {
-	if t.Root == nil {
-		return false
-	}
-	return t.Root.do(fn)
-}
-
-func (n *Node) do(fn func(e *Elem) bool) (done bool) {
-	if n.Left != nil {
-		done = n.Left.do(fn)
-		if done {
-			return
-		}
-	}
-	done = fn(n.Elem)
-	if done {
-		return
-	}
-	if n.Right != nil {
-		done = n.Right.do(fn)
-	}
-	return
-}