Relative url values in .gitmodules confusingly sensitive to clone via ssh vs https.

[Benjamin Shropshire <benjamin.shropshire@economicmodeling.com>]

From my perspective, this is a bug.

If I clone a repo twice like this:

git clone https://github.com/user/repo.git ./https
git clone git@github.com:user/repo.git ./ssh

And if it contains a .gitmodules like this:

[submodule "x"]
    path = xxx
    url = ../../different-user/something.git

When I `git submodule update --init --recursive` in each, only the
HTTPS version works. the SSH version confusingly seems to try to find
something at ~/different-user/something.git or some other path in the
local file system.

this seems consistent with the URL parsing resulting in different
segmentation and thus the ../../ ending up in different places:

https =[..., 'github.com', 'user', 'repo.git']
ssh=['git@github.com:user', 'repo.git']

# ../../
https[:-2] -> [..., 'github.com']
ssh[:-2] -> []

This theory is supported by the fact that this works:

git clone ssh://git@github.com/user/repo.git ./ssh
cd ssh
git submodule update --init --recursive

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See also: https://stackoverflow.com/questions/36564696/how-to-use-same-protocol-for-git-submodules