procedure to check equality of list-elements

[Thomas Morley]

Hi,

in !1701 `ly:beam::calc-knee' checks whether all list-elements are equal.
Basically doing (apply eqv? <number-list>).
Tbh, I don't understand why it works...
Though, the need to check a list for all list-elements are equal
happened to me not only once.
Thus, would it be acceptable to add something like:

(define* (equal-list-elts? list #:optional (proc eq?))
  (apply proc list))

to lily-library.scm?

Cheers,
  Harm