bug#70959: Tramp connection property can interact weirdly with cache

[Dmitry Gutov <dmitry@gutov.dev>]

I've used the recipe for "direct-async-processes" as suggested:

(add-to-list 'tramp-connection-properties
              (list (regexp-quote "/ssh:user@host:")
                    "direct-async-process" t))

and at first (the connection was already open) it didn't take effect. I 
think I had to kill the connection buffer for the new property to be 
used. Would be nice if this was instant.

But also, after that I tried altering tramp-connection-properties back 
to disable direct-async-process for that host (for the purposes of 
testing and measuring things more precisely), and found that changing 
the variable doesn't bring the new behavior back. Restarting Emacs 
didn't bring the old (non-direct) behavior back either - I had to edit 
the ~/.emacs.d/tramp file by hand to remove that property.

I think that's something that might confuse other users.