Bender override issue

[meggiman]

When using version override in a Bender.local file, Bender behaves inconsistent to a normal version declaration:
Let's assume the following Bender.yml file of a sub-dependency:

...
dependencies:
  foo: {git: "https://github.com/foo/foo.git", version: 0.3.0} # version 0.3.0 = commit-id "abcd"

and the following override file:

overrides:
  foo: {git: "https://github.com/foo/foo.git", rev: "1234"}

If we call bender update followed by bender path foo we get the following:

/......../.bender/git/checkouts/foo-abcd

Inspecting this directory reveals, that bender checked out commit 1234 within the foo-abcd directory. First of all, this is unintuitive because the user would expect bender to generate a new version directory like it does for any other (not overriden) dependency.
The second problem is: If commit 1234 does not exist, bender update will not error out but will just keep using commit version abcd without notifying the user about the non existent override version 1234.

Expected behavior: Bender should create new directories for override versions and show an error message if it cannot find the commit referenced in an override.