I had problems to locate the source code repository. I could find one on Bitbucket, it is linked from Codeigniter wiki (scroll down to "Mercurial Server"): Codeigniter Reactor / license.txt
That's the information to gather from my point of view. And it's what has been already commented to your question: "Why not contact application authors?" and the pointer to the License in the Codeigniter user-guide.
Indeed this is not a GPL v3 license but looks more like a MIT/New BSD-Style license with some additions for the concrete trademarks/names somewhat reserved by Ellislab Inc. .
From what you describe in your question I just think you're not referring to the right codebase.
I was unable to find the source location you named (Google Code), so I can not say much about it. But from what you describe I assume that the code might be either a fork or a derivate of an older version of the framework. As the framework can be integrated into other applications as well, probably that's another application making use of it.
As the license is kind of New-BSD-Style, it's possible to release a derivate under another license incorporating the Codeigniter code with it's own (sublicensing).
Probably that has happened with the code base you named, but as I don't have any link to it, this is only a guess. Technically this should be possible.
So for yourself to get some satisfaction with your open questions, I suggest the following:
- Locate the source-code you want to make use of. Refer to the most "official" source, e.g. get as close to the main project as you can get for the code in question.
- This has the benefit that it's easier to clarify the actual licensing terms.
- And it has the benefit as this is a framework/library, that you actually get the most stable version of the code (as this is an active project).
- Locate the licensing terms. I do not know much about licensing of the Codeigniter project, so it might indeed be useful to clarify some questions with the original author(s):
- Is the whole package available under the same licensing terms?
- Or are parts of the package under additional / different licensing terms?
I think if you get these questions clarified you've really done a lot. Somehow document your progress so you actually have reference in case you need that.
However from my own point of view, I would say, that the license information given on the Codeigniter homepage is quite explicit. And if I take an exemplary look into a source-file like
/system/libraries/Ftp.php I would say it's really clearly documented in file headers as well. So actually not really something to worry about.