bug#19556: eww: make URI rewriting fully customizable

[Eli Zaretskii <eliz@gnu.org>]

> From: Ivan Shmakov <ivan@siamics.net>
> Date: Sat, 10 Jan 2015 14:40:57 +0000
> 
> >>>>> Eli Zaretskii <eliz@gnu.org> writes:
> >>>>> From: Ivan Shmakov  Date: Sat, 10 Jan 2015 13:17:55 +0000
> 
> […]
> 
>  > Why put the "standard" rules into the defcustom?
> 
> 	So to make the tricks played by EWW on unsuspecting URIs more
> 	obvious to the user.

How does that make it more obvious?

>  > That's what hooks are normally for -- _modifying_ the default
>  > behavior, not supplanting it.
> 
> 	Are they?  For instance, when run with -Q, my find-file-hooks
> 	includes ange-ftp-set-buffer-mode, epa-file-find-file-hook,
> 	vc-find-file-hook

None of these replace the default behavior of their hookee functions.
They _add_ something to it.  The default behavior is not in the hook,
it's in the code that calls the hook.

And anyway, I said "normally", so a couple of examples to the contrary
doesn't yet invalidate what I said.

> 	With these functions being explicitly listed, however, I could
> 	easily drop everything but vc-find-file-hook off the list to get
> 	rid of the functionality that tends to get in my way.

It sounds like we have some deep disagreement about what the hooks are
for.  You want a hook to _remove_ some behaviors, but that's not what
hooks are for.

> 
>  > E. g., with your suggestion, what happens if someone customizes the
>  > value to nil?
> 
> 	That’s simple: M-x eww will assume that the URIs it’s given
> 	never need any special treatment.

Which is clearly wrong with some URIs.

Please let's not go that way.