bug#2756: move SCCS later in vc-handled-backends

[Stefan Monnier]

>> > SCCS should be moved after later in the vc-handled-backends list, after
>> > the modern VCs.
>> > Opening any file costs a call to vc-sccs-registered
>> > vc-sccs-search-project-dir (and whatever they call).
>> 
>> No matter where SCCS is in the vc-handled-backends list, those functions
>> will be run for any file that is not version controlled, which is likely
>> to be a very common case.
>> 
>> > SCCS is not really popular nowadays,
>> 
>> Same thing for RCS, indeed.
>> 
>> > and that should be reflected on the vc-handled-backends list.
>> 
>> We could remove backends from the list based on the presence/absence of
>> the corresponding executable(s).

> Would that be acceptable for 23.1?

No.

> If not, let's go for fixing the easier problem: moving SCCS later in the
> list of backends.

What problem?  And in what way is it a fix for it?


        Stefan