message: Updated vfs tests.
  Turns out the 'length' of a directory is platform-dependent and generally
  undefined.  Fair enough!
diff: @@ -136,8 +136,13 @@ pub trait VFS: Debug {
  }
  pub trait VMetadata {
  + /// Returns whether or not it is a directory.
  + /// Note that zip files don't actually have directories, awkwardly.
  fn is_dir(&self) -> bool;
  + /// Returns whether or not it is a file.
  fn is_file(&self) -> bool;
  + /// Returns the length of the thing. If it is a directory,
  + /// the result of this is undefined/platform dependent.
  fn len(&self) -> u64;
  }
  @@ -771,7 +776,12 @@ mod tests {
  assert!(!m.is_file());
  assert!(m.is_dir());
  // Not exactly sure what the "length" of a directory is, buuuuuut...
  - assert_eq!(m.len(), 18);
  + // It appears to vary based on the platform in fact.
  + // On my desktop, it's 18.
  + // On Travis's VM, it's 4096.
  + // On Appveyor's VM, it's 0.
  + // So, it's meaningless.
  + //assert_eq!(m.len(), 18);
  }
  {
  