Fix dependency error propagation by replaying the panic

[a-palchikov]

Persist the panic that a dependency had failed with and replay it each time (*onceFun).run is invoked.

I took the liberty of restructuring runDeps to be more idiomatic by using channels but let me know if that's beyond the scope.

Fixes https://github.com/magefile/mage/issues/371.

[jippi]

I've been hit with this issue a couple of times, @natefinch do you think it need more work before being merged in?

[natefinch]

Let me look at this tonight. I'll make time for it. Sorry for the delay