slide-out checks out the parent of the topmost slid-out branch, even if the current branch hasn't been slid out

[PawelLipski]

The behavior of checking out the parent (i.e. a non-slid-out branch) makes sense when the current branch has been slid-out... but is confusing/surprising otherwise.

Easiest to repro:

master
  foo
  bar

Check out foo, then git machete slide-out bar.
Expected: foo is still checked out
Actual: master is checked out