Git extension doesn't see external worktree

[usr-sse2]

Steps to reproduce:

git clone --bare <some repository with a C# project> ~/bare.git
cd ~/bare.git
git worktree add ~/worktree master
open ~/worktree/<solution file> -a "Visual Studio (Preview).app"

Expected behaviour:
VS for Mac allows to commit, show history etc. from the Version control menu

Actual behaviour:
Version control integration is inactive

[Therzok]

This is a limitation by us having an outdated libgit2. We're in the process of upgrading to 0.26 here.

But it'll take a bit more to upgrade to 0.27, which has worktree support, as 0.27 does not work correctly (there's some memory corruption going on).

[Therzok]

On the memory corruption, see:
github/VisualStudio#1315

[Therzok]

Actually, unrelated. Okay, so, what's going on is that, for some reason, libgit2 decides to go over bounds with memory, and write the repo pointer in a tree to 9.

I suppose this is an overflow issue, because of lack of type safety in C.

@sevoku ^^