GitHub user/repo names are case insentitive. This can cause issues when dealing with
repos programmatically using systems that aren't aware of this (e.g. go packages).
This commit updates the cloning logic of the CLI to query the API for the canonical
capitalization and uses that for the clone operation.
Fixes: #1845
This commit hacks the existing repo clone tests into something usable by
the new isolated command. It went ok and was less effort than trying to
introduce the same kind of test format as repo view and gist create.
