git-rev-parse incorrectly uses --default parameter when invalid revision is supplied

[Brandon Casey <casey@nrlssc.navy.mil>]

When rev-parse is called with an invalid revision parameter and
--default has been used to set a default revision, the output
will be based on the parameter to --default.

For example:

  This likely fails:
    $ git rev-parse --verify foobar
    fatal: Needed a single revision

  This likely succeeds but probably should fail:
    $ git rev-parse --verify --default refs/heads/master foobar
    b2e62a7dc6ba20a354d7590bf6a1d9264de7efe3


The documentation for rev-parse says:
   --default <arg>::
         If there is no parameter given by the user, use `<arg>`
         instead.


git-stash uses this command, so a typo could cause the wrong stash
to be applied.

   git stash apply stsh@{1}

If stash@{0} exists, it will be applied which is definitely not
what the user would want.

It is not straight forward to me how to modify builtin-rev-parse.c
to fix this.

-brandon