Add ccl:*lisp-exit-functions* or change behavior of ccl:*lisp-cleanup-functions* or document image hooks

[jlawrence]

I was surprised that ccl:save-application called ccl:*lisp-cleanup-functions* before saving the image. I expected a snapshot of the current image (this is the behavior of other implementations), not an image in a post-shutdown state.

I can use ccl:*save-exit-functions* to save the desired state, or restore state with ccl:*lisp-startup-functions*, but neither may be easy in general.

If it is decided that the current behavior is preferred, then at least document it in ccl:save-application or elsewhere, as it differs from other implementations.