Update libgit2 binaries to 40a6051

https://github.com/libgit2/libgit2/compare/5f9f69d...40a6051
Make LambdaEqualityHelper.Equals symmetric when exactly one argument is null
Remove the empty implementation of SafeHandleBase.Dispose (overrides SafeHandle.Dispose) from release builds
Teach Network to list references on a remote
Enhance repo.Refs.IsValidName test coverage
Introduce repo.Network.Remotes.IsValidName()

Fix #317
Alpha sort signatures of native methods
Enhance repo.NetWork.Remotes.Add() test coverage

Fix #318
Guard against null remote names
Allow retrieval of the Remote of a non local branch
Add strongly typed NonFastForward exception
Micro-optimization: use new List<>(capacity)
Add StageLevel to IndexEntry.DebuggerDisplay
Use readonly for applicable fields
Remove inferable delegate construction
Remove redundant qualifiers
Remove unused usings
Dismiss a few other R# warnings
Add missing XML comments
Introduce Repository.Conflicts