Implement git refs API for listing references (branches, tags and other) (#5354)

* Inital routes to git refs api

* Git refs API implementation

* Update swagger

* Fix copyright

* Make swagger happy add basic test

* Fix test

* Fix test again :)

vendor/gopkg.in/src-d/go-git.v4/prune.go

@@ -0,0 +1,66 @@
+package git
+
+import (
+	"errors"
+	"time"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
+)
+
+type PruneHandler func(unreferencedObjectHash plumbing.Hash) error
+type PruneOptions struct {
+	// OnlyObjectsOlderThan if set to non-zero value
+	// selects only objects older than the time provided.
+	OnlyObjectsOlderThan time.Time
+	// Handler is called on matching objects
+	Handler PruneHandler
+}
+
+var ErrLooseObjectsNotSupported = errors.New("Loose objects not supported")
+
+// DeleteObject deletes an object from a repository.
+// The type conveniently matches PruneHandler.
+func (r *Repository) DeleteObject(hash plumbing.Hash) error {
+	los, ok := r.Storer.(storer.LooseObjectStorer)
+	if !ok {
+		return ErrLooseObjectsNotSupported
+	}
+
+	return los.DeleteLooseObject(hash)
+}
+
+func (r *Repository) Prune(opt PruneOptions) error {
+	los, ok := r.Storer.(storer.LooseObjectStorer)
+	if !ok {
+		return ErrLooseObjectsNotSupported
+	}
+
+	pw := newObjectWalker(r.Storer)
+	err := pw.walkAllRefs()
+	if err != nil {
+		return err
+	}
+	// Now walk all (loose) objects in storage.
+	return los.ForEachObjectHash(func(hash plumbing.Hash) error {
+		// Get out if we have seen this object.
+		if pw.isSeen(hash) {
+			return nil
+		}
+		// Otherwise it is a candidate for pruning.
+		// Check out for too new objects next.
+		if !opt.OnlyObjectsOlderThan.IsZero() {
+			// Errors here are non-fatal. The object may be e.g. packed.
+			// Or concurrently deleted. Skip such objects.
+			t, err := los.LooseObjectTime(hash)
+			if err != nil {
+				return nil
+			}
+			// Skip too new objects.
+			if !t.Before(opt.OnlyObjectsOlderThan) {
+				return nil
+			}
+		}
+		return opt.Handler(hash)
+	})
+}