use aliases in all keys list to enable proper Unmarshaling

viper.go

@@ -1149,6 +1149,10 @@ func (v *Viper) AllKeys() []string {
 		m[strings.ToLower(key)] = struct{}{}
 	}
 
+	for key, _ := range v.aliases {
+		m[strings.ToLower(key)] = struct{}{}
+	}
+
 	a := []string{}
 	for x, _ := range m {
 		a = append(a, x)

viper_test.go

@@ -838,3 +838,28 @@ func TestMergeConfigNoMerge(t *testing.T) {
 		t.Fatalf("fu != \"bar\", = %s", fu)
 	}
 }
+
+func TestUnmarshalingWithAliases(t *testing.T) {
+	SetDefault("Id", 1)
+	Set("name", "Steve")
+	Set("lastname", "Owen")
+
+	RegisterAlias("UserID","Id")
+	RegisterAlias("Firstname","name")
+	RegisterAlias("Surname","lastname")
+
+	type config struct {
+		Id int
+		FirstName string
+		Surname string
+	}
+
+	var C config
+
+	err := Unmarshal(&C)
+	if err != nil {
+		t.Fatalf("unable to decode into struct, %v", err)
+	}
+
+	assert.Equal(t, &C, &config{Id: 1, FirstName: "Steve", Surname: "Owen"})
+}