Rename the revwalk constructor Walk() -> NewRevWalk()

This makes it be more in line with Go conventions and uses its full
name.

repository.go

@@ -154,7 +154,7 @@ func (v *Repository) CreateSymbolicReference(name, target string, force bool) (*
 	return newReferenceFromC(ptr), nil
 }
 
-func (v *Repository) Walk() (*RevWalk, error) {
+func (v *Repository) NewRevWalk() (*RevWalk, error) {
 	walk := new(RevWalk)
 	ecode := C.git_revwalk_new(&walk.ptr, v.ptr)
 	if ecode < 0 {

walk_test.go

@@ -10,7 +10,7 @@ func TestWalk(t *testing.T) {
 	defer os.RemoveAll(repo.Workdir())
 	commitId, _ := seedTestRepo(t, repo)
 
-	walk, err := repo.Walk()
+	walk, err := repo.NewRevWalk()
 	checkFatal(t, err)
 	walk.Push(commitId)
 	walk.Sorting(SortTime | SortReverse)