More accurate git-svn detection.

Hello, i'm using git-repo tool, the one Google Android projects provides. Basic it organize and manage multiple git repos using symbolic links and hard links. There's a small issue: git-repo always create .git/svn links, even if it's empty inside. Which basically turns TortoiseGit into GitSvn mode unnecessarily.

So i wonder if we can improve the detection of git-svn by checking if there's actually a file in the .git/svn directory? (The code is in Git/TGitPath.cpp, in CTGitPath::HasGitSVNDir() and CTGitPath::GetAdminDirMask(), i'm not sure if there's any others)

Or optionally, provide a way to disable the default DCommit option in Commit execution result dialog?

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