refs/files: fix issues with git-fetch on case-insensitive FS#798

dscho wants to merge 4 commits intomicrosoft:vfs-2.51.0microsoft/git:vfs-2.51.0from

gitgitgadget:kn/refs-files-case-insensitivegitgitgadget/git:kn/refs-files-case-insensitiveCopy head branch name to clipboard