protect compile-time side-effects of DEFUN with a package-lock

protect compile-time side-effects of DEFUN with a package-lock

  Ie. proclaiming as a function, possibly nuking existing inline
  definitions.

  Fixes lp#675584.

  Now compiling a file with

    (DEFUN LOCKED:FOO ...)

  signals a compile-time error.

    (WITHOUT-PACKAGE-LOCKS (DEFUN LOCKED:FOO ...))

  still works, as the DEFUN stops being a toplevel form, and hence no
  longer has compile-time side effects except for those inherent to
  compiling a NAMED-LAMBDA.