Refactor of paths detection

[vonalbert]

Hello everyone, I'm aware you're not accepting contributions from the public, but i want to share my 5 cents, and you're free to reject these changes. Following there is a list of the changes and the motivations for each one:

1. Maybe it's better to ensure the current directory is always the FC path
2. is_dir checks both relative and absolute paths so we only need to check if the $system_path and $application_folder are valid directories and then save the constant using realpath
3. realpath(DIR) is redundant because as far as i know DIR === realpath(DIR)
4. I'm removing the check of application folder inside the system folder because it's an unnecessary operation, since it could be done setting the $application_folder variable to 'system/application';
5. There's no need to replace the directory separators before apply a realpath because the substitution is provided by realpath itself (maybe is it there for the realpath's caching features?)

[lonnieezell]

First off, thanks. I hadn't taken the time to look through this logic, yet, but had largely just copied it from CI3. Looks like there is definitely some logic in here that's not needed, like the application directory inside of system folder, which can be simplified or removed. Some of them, though, I get the feeling there was a reason at one time, but some of those issues might have been resolved in newer versions of PHP.

1. I can't think of a problem with this one.
2. I'm trying to think of a reason why this logic would have been in place, and can't come up with it, since realpath ensures that all directories have executable permissions. Unless it has something to do with open_basedir restrictions returning false during a realpath, when it's still perfectly executable?
3. Looking at PHP docs, I think this might be incorrect. Docs say the DIR is identical to dirname(FILE). Looking at dirname, then, we see this line: "dirname() operates naively on the input string, and is not aware of the actual filesystem". So we need to keep this check, it sounds like.
4. Absolutely agree with this. Appears this was here specifically for ExpressionEngine support in days gone by.
5. I'm not 100% on this one. All of the examples that I've seen regarding Windows has it being substituted as we currently do. Whether or not that's still required in PHP7, I don't know. This warrants more research.

@narfbg Do you have any idea about the validity or necessity of these, especially 2 and 5?

[narfbg]

1. If realpath() was flawless, these checks wouldn't exist ... obviously somebody had a problem with it. Don't know what exactly.
2. CI3 doesn't have that.

[lonnieezell]

Are your 1 and 2 supposed to match up with the above numbering system, or just general points?

If they are supposed to match up, then this is what I was taking 2 to refer to.

[narfbg]

Huh ... that's Markdown's fault. I wrote 2 and 5 respectively.

[lonnieezell]

Ah, that makes more sense then. And 5 has been a recent change, IIRC. This code came directly from CI3 originally. Good to know we can clean that up a little, though.

[narfbg]

Not directly ... you've made some modifications to it and 5 is part of them. :)

[lonnieezell]

Oh, that's right. Realpath wasn't used there and I had a brainfart one night thinking that might help improve the realpath caching of files so scattered a few likely useless realpath's around. :)

[vonalbert]

Oh didn't know 5 was already fixed in the official repo.

So for 3, unless i'm missing some edge cases i'm not aware of, DIR should always exists. Anyway no probs for me in leaving it at his place. I'm referring to
define('FCPATH', realpath(__DIR__).DIRECTORY_SEPARATOR);
Anyway I found this stackoverflow link on this subject
http://stackoverflow.com/questions/9415940/is-realpath-redundant-in-absolutepath-realpath-dir-is-dir-always

For 2 I'll research more this evening if you feel it requires modifications.

[vonalbert]

Added this to ensure $system_path (and $application_folder below) have executable permissions

[lonnieezell]

I'm going to go ahead and merge this for now. Firing up Parallels to be able to check it out under Windows, also. This is something we'll need to keep an eye on, but I do like the simplifications.

Thanks.