Remove easy compilation warnings so we can concentrate on real ones.

Most of the warnings were in contribs and were due to direct `cl'
usage. Others were a simple product of bitrot and abandonment. Made
the easy fix when it was obvious, added notes when I'm pretty sure I
broke something.

* slime.el: Require 'cl but only when compiling.

* contrib/bridge.el (bridge-insert-function): Add it.
(bridge-insert): Use it.

* contrib/slime-asdf.el: Require 'grep. fix byte-compilation warnings.

* contrib/slime-autodoc.el: Require 'eldoc. Fix byte-compilation warnings.
(slime-autodoc-mode): Don't use `interactive-p'

* contrib/slime-cl-indent.el: Move definitions around to fix
byte-compilation warnings.
(common-lisp-current-package-function): Make it a variable. It's
used as such.
(slime-cl-indent): Provide it.

* contrib/slime-clipboard.el (slime-clipboard-redisplay): Add FIXME note
after removal of `slime-clipboard-insert-entries'.

* contrib/slime-compiler-notes-tree.el (slime-clipboard-entry-at-point):
Fix byte-compilation warnings.

* contrib/slime-enclosing-context.el: Fix byte-compilation warnings and
explain why it has been broken since 2010.

* contrib/slime-fontifying-fu.el: Fix byte-compilation warnings, but
probably broken since a long time.

* contrib/slime-fuzzy.el: Fix byte-compilation warnings.

* contrib/slime-indentation.el: Fix byte-compilation warnings.

* contrib/slime-mdot-fu.el: Fix byte-compilation warnings.

* contrib/slime-mrepl.el: Fix byte-compilation warnings.

* contrib/slime-package-fu.el: Fix byte-compilation warnings.

* contrib/slime-presentations.el (slime-presentation-bridge-insert): Use
this new function, instead of redefinition.

* contrib/slime-references.el: Fix byte-compilation warnings.

* contrib/slime-sprof.el: Fix byte-compilation warnings.

* contrib/slime-tramp.el: Fix byte-compilation warnings.

* lib/hyperspec.el: Fix byte-compilation warnings.