Implement complexSelectorHasExtension for debug mode to check if a selector has an extension before running through the extend logic. This is mainly to get our printing to match up with ruby sass, which is why it is debug only. ruby sass only runs extend on selectors with extensions. However, libsass runs it on all selectors. The result of the extend code is the same selector if the selector doesn't have an extension, so this doesn't need to happen in release mode.