disable the other sb-sprof test on darwin as well *sigh*
package local nicknames

  Example terminal session using Linedit:

    * (defpackage :foo (:use :cl) (:local-nicknames (:sb :sb-ext)))

    #<PACKAGE "FOO">
    * (in-package :foo)

    #<PACKAGE "FOO">
    * (sb:posix-
    sb:posix-environ  sb:posix-getenv
    * (sb:posix-getenv "USER")

    "nikodemus"

  API:

    function PACKAGE-LOCAL-NICKNAMES package
    function ADD-PACKAGE-LOCAL-NICKNAME nick global &optional package
    function REMOVE-PACKAGE-LOCAL-NICKNAME old-nick &optional package

    DEFPACKAGE option: (:local-nicknames {(local-nick global-name)}*)

  Design issues and considerations:

   * Nicknames are late-bound. This is seems good for usability and
     also keeps the implementation simple. Causes ugliness in
     printing, though.

   * "CL", "COMMON-LISP", "KEYWORD", and "" cannot be used as local
     nicknames. I think this is good for sanity, but not strictly
     required. Because of the way (find-package :keyword) is
     idiomatically used to guarantee print/read consistency across
     packages, I think it at least should be protected.

   * To preserve read/print consistency, we use package local nicknames
     as prefixes when printing.

   * The hook into FIND-PACKAGE is invisible. An alternative solution
     would be to add FIND-PACKAGE-USING-PACKAGE, but that would not
     work out of the box with arbitrary existing code: see for example
     how nicely Linedit was able to utilize the sb: prefix without
     any changes to it.

   * Local nicknames are protected by package locks.

   * If you want to bypass nicknames, you need to first get into
     a known package without nicknames. There could be an explicit
     way as well, but not sure if that's needed or a good idea.

  Random crap mixed in:

     Re-order DEFPACKAGE option docs in rough order of usefulness.
add :local-nicknames to *features*
make ADD-PACKAGE-LOCAL-NICKNAME provide restarts for its errors

  So those who want can play overriding CL, etc.
express FIND-PACKAGE in terms of FIND-PACKAGE-USING-PACKAGE

  Unexported and undocumented, but waiting for Christophe...

  Also document local nicknames in FIND-PACKAGE.