bug#26540: 25.2; [PATCH] Add cl-set-equal to test for set equality

[Drew Adams]

> This is admittedly bikeshedding, for which I apologize, but I'd like to
> mention the possibility of adding this to `seq' as an alternative to
> adding it to `cl-lib'.
> 
> My two arguments for adding it to `seq' are:
>   - This function doesn't exist in Common Lisp, so `cl-lib' seems like
>     a somewhat arbitrary place for it, other than that its
>     implementation uses `cl-set-exclusive-or'.

Agreed.  This is not Common Lisp emulation.  It does not
belong in a cl*.el library and should not have the `cl-'
prefix.