Don't bind byte-compile-warnings while autoloading 'bytecomp.

* slime.el (slime--byte-compile): New function.
(slime--compile-hotspots): Use it.

* slime-repl.el: Load 'bytecomp before binding byte-compile-warnings.
* slime-scratch.el: eval-and-compile is redundant around require.
* inferior-slime.el: Whitespace cleanup.