Report a style warning when :USE is omitted from DEFPACKAGE

[Paul F. Dietz]

The defaulting behavior of :USE in DEFPACKAGE is implementation dependent, and as a result is not portable. Issue a style warning if DEFPACKAGE is found without a :USE clause.

[Paul F. Dietz (paul-f-dietz)]

This issue tripped up phoe when he was producing a portable test suite for package local nicknames. Perhaps it should be a warning, not a style warning.

[Douglas Katzman (dougk)]

There is set of users who would be disaffected - those who compile in a build infrastructure that escalate all warnings to build breakages. Introducing a new warning for something as innocuous as a perfectly ordinary call to defpackage that is nowise unstylish would kind of be a problem for them.
(And don't get me wrong - it is problematic to introduce _any_ new style warning)