sage: 8.9.beta9 -> 8.9.rc0

Sage now by default expects the lcalc library to be named Lfunction
(instead of libLfunction). This could be changed by an environment
variable (https://trac.sagemath.org/ticket/28224), but various distros
seem to agree on this standard
(https://groups.google.com/forum/#!topic/sage-packaging/xvh55IxHTZg) so
it's best just to follow it. The old standard was set by sage anyway and
sage is the only consumer of lcalc in nixpkgs.