Don't load plugins starting with "Microsoft."
GitModule minor refactoring

Open .git/config fixed
WorkingDirGitDir() replaced by GetGitDirectory()
` + AppSettings.PathSeparator.ToString() + ` replaced by `Path.Combine()`
FixPath replaced by ToPosixPath()
AppSettings.PathSeparator replaced by Path.DirectorySeparatorChar
` + Path.DirectorySeparatorChar` replaced by EnsureTrailingPathSeparator()
Implemented additional PathUtil methods
Merge branch 'feature/path-util'