Add support for relative submodules

Currently there is no support for submodules where the url starts with ./ or ../, it will fail with an Routing Error. This is required is you don't want to force a submodule to ssh or http usage.

For a given Repository http://server/group/root.git

---

[submodule "sub1"] path = sub1 url = ../submodule.git

Wrong: http://server/group/ root /submodule.git Correct: http://server/group/submodule.git

---

[submodule "sub2"] path = sub2 url = ../../any/submodule.git

Wrong: http://server/ group/any /submodule.git Corrent: http://server/any/submodule.git