[PATCH setup] Query the user if a corrupt local file is found

[Ken Brown]

On 12/16/2017 1:37 PM, Ken Brown wrote:
> If a corrupt file is found in one of the selected mirror site
> directories, offer to delete it instead of making this a fatal error.
> Do this only on the first call to check_for cached().  If the corrupt
> file is still there on the second call, then the deletion failed, and
> the user will have to fix the problem.
> 
> See https://cygwin.com/ml/cygwin/2017-12/msg00122.html for discussion.

This is unnecessarily complicated.  Please disregard.  I'll submit v2 later.

Ken