AreDirsEqual recursively compares two directories for equality NOTE: filepath.Wale guarantees lexical order traversal (elements already ordered) thus allowing us to use a slice as opposed to a map.

MakeAferoTestFs is a convenience function that lets you construct many directories and files in an afero in-memory filesystem by passing a single path->contents map.

MakeTempTestDir is used to populate a temporary directory with the file/directory contents specified in filesMap.