Evaluate dumper-action-forms in CL-USER package.

Currently the dumper-action-forms are evaluated in the (gensym "DUMPER") package. This creates the possibility for missing package errors when load is executed later, both in the built image and in unrelated images. Here's a minimal example that triggers the undesirable behavior which this patch fixes:

    buildapp \
        --eval "(load (compile-file \"test.lisp\"))" \
        --output ~/bin/irrelevant 

    ;;;; test.lisp

    (print 'foo)

    ;;;;  load the fasl buildapp created from test.lisp into any image.
    * (load "test")

    debugger invoked on a SB-KERNEL:SIMPLE-PACKAGE-ERROR in thread
    #<THREAD "main thread" RUNNING {1002AC3153}>:
      The name "DUMPER697" does not designate any package.