Remove Leaks configuration

Fix #869
Honour ThreadAffinity in Proxy.git_odb_exists
Fix for computing blob size without loading entire blob content in memory - Fix #873
Teach Repository.Clone to accept a specific branch to checkout
Improve tracking toolset of improperly released unmanaged handles
Prevent leaking DiffSafeHandle on UnmatchedPathException
Include LibGit2Sharp.sln.DotSettings migration change
Minor cleanups
Update libgit2 to 19ae843

https://github.com/libgit2/libgit2/compare/3f8d005a82b39c504220d65b6a6aa696c3b1a9c4...19ae843937bed26ddf522a4eb00953c81b1a4561
Fix Diff Lines truncation.