Replace Unsafe with Strict mechanism

Previously by default the presence of a missing field in
a udt would result in an error reported. The Unsafe
mechanism could be used to ignore these fields.

This PR changes the default behavior to ignoring missing
fields and only reporting an error if Strict mode is used.
This approach is in line with the gocql.

udt.go

@@ -26,14 +26,14 @@ var (
 type udt struct {
 	field  map[string]reflect.Value
 	value  reflect.Value
-	unsafe bool
+	strict bool
 }
 
-func makeUDT(value reflect.Value, mapper *reflectx.Mapper, unsafe bool) udt {
+func makeUDT(value reflect.Value, mapper *reflectx.Mapper, strict bool) udt {
 	return udt{
 		value:  value,
 		field:  mapper.FieldMap(value),
-		unsafe: unsafe,
+		strict: strict,
 	}
 }
 
@@ -42,7 +42,7 @@ func (u udt) MarshalUDT(name string, info gocql.TypeInfo) ([]byte, error) {
 	if ok {
 		return gocql.Marshal(info, value.Interface())
 	}
-	if u.unsafe {
+	if !u.strict {
 		return nil, nil
 	}
 	return nil, fmt.Errorf("missing name %q in %s", name, u.value.Type())
@@ -53,25 +53,25 @@ func (u udt) UnmarshalUDT(name string, info gocql.TypeInfo, data []byte) error {
 	if ok {
 		return gocql.Unmarshal(info, data, value.Addr().Interface())
 	}
-	if u.unsafe {
+	if !u.strict {
 		return nil
 	}
 	return fmt.Errorf("missing name %q in %s", name, u.value.Type())
 }
 
 // udtWrapValue adds UDT wrapper if needed.
-func udtWrapValue(value reflect.Value, mapper *reflectx.Mapper, unsafe bool) interface{} {
+func udtWrapValue(value reflect.Value, mapper *reflectx.Mapper, strict bool) interface{} {
 	if value.Type().Implements(autoUDTInterface) {
-		return makeUDT(value, mapper, unsafe)
+		return makeUDT(value, mapper, strict)
 	}
 	return value.Interface()
 }
 
 // udtWrapSlice adds UDT wrapper if needed.
-func udtWrapSlice(mapper *reflectx.Mapper, unsafe bool, v []interface{}) []interface{} {
+func udtWrapSlice(mapper *reflectx.Mapper, strict bool, v []interface{}) []interface{} {
 	for i := range v {
 		if _, ok := v[i].(UDT); ok {
-			v[i] = makeUDT(reflect.ValueOf(v[i]), mapper, unsafe)
+			v[i] = makeUDT(reflect.ValueOf(v[i]), mapper, strict)
 		}
 	}
 	return v