Better errors for package operations.

Add some missing errors, make other errors to be of type
sb-kernel:simple-package-error.

Fixes lp#1154776.

DELETE-PACKAGE should be signalling a continuable error, but wasn't
since 1.0.37.44.
Accessing &MORE arguments checks bounds.

(funcall (lambda (&rest args) (car args))) => garbage,
because &more accessing didn't check bounds.

Fixes lp#1154946.
Optimize CAD*R for &MORE args.

Call %rest-ref when possible, and SECOND-FOURTH are optimized by
extension too.