Setting "services.lighttpd.gitweb.enable" to true doesn't enable the
required lighttpd modules to actually make it work. The problem is that
"or" and "||" don't mean the same thing: "or" falls back to the second
operand if the first is not defined, whereas "||" is the normal logical
operator. When cfg.cgit.enable is defined, as false, the expressions
don't have the desired effect.
[Bjørn: modify commit message]
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
