Fixed prettify-symbols-mode bug

[ghollisjr]

Fix for the bug described in Issue #437

[luismbo]

Could you explain, perhaps in the commit message, what is going on? TIA.

[luismbo]

Ah, I see you've written down your investigation in #437. A cursory look at that raises the question: is this something that could be fixed in prettify-symbols-mode instead?

[ghollisjr]

Unfortunately not, the issue is that prettify-symbols-mode uses font-lock-mode to manage symbol substitution & highlighting, and SLIME functions didn't use the font-lock-mode setting variables which are needed because font-lock-mode essentially shadows the usual variables. The font-lock-* variables are pretty much 1-to-1 replacements and just need to be managed in parallel to guarantee interoperability with font-lock-mode-based modes.

So I added those variables to the SLIME functions and now SLIME works with or without prettify-symbols-mode/font-lock-mode.

I mentioned a small blemish in the REPL coloring when using prettify-symbols-mode, but that's specifically a prettify-symbols-mode issue and can't be helped from SLIME's side due to prettify-symbols-mode treating the REPL buffer as any other buffer, so output gets treated like code by the syntax coloring algorithm.