remove build tag from extention methods

Author: PeterIvanov

error.go

@@ -156,6 +156,25 @@ func (e *Error) Cause() error {
 	return e.cause
 }
 
+// Is returns true if and only if target is errorx error that passes errorx type check against current error.
+// This behaviour is exactly the same as that of IsOfType().
+// See also: errors.Is()
+func (e *Error) Is(target error) bool {
+	typedTarget := Cast(target)
+	return typedTarget != nil && IsOfType(e, typedTarget.Type())
+}
+
+// From errors package: if e.Unwrap() returns a non-nil error w, then we say that e wraps w.
+// Unwrap returns cause of current error in case it is wrapped transparently, nil otherwise.
+// See also: errors.Unwrap()
+func (e *Error) Unwrap() error {
+	if e.cause != nil && e.transparent {
+		return e.cause
+	} else {
+		return nil
+	}
+}
+
 // Format implements the Formatter interface.
 // Supported verbs:
 //