Before that, as it was given an empty configuration file, nscd would
actually have all its caches disabled.
* gnu/services/base.scm (<nscd-configuration>, <nscd-cache>): New record
types.
(%nscd-default-caches, %nscd-default-configuration): New variables.
(nscd.conf-file): New procedure.
(nscd-service): Add 'config' parameter. Use 'nscd.conf-file', and
pass its result as the '-f' parameter of nscd.
* doc/guix.texi (Base Services): Update 'nscd-service' documentation
accordingly. Document 'nscd-configuration', 'nscd-cache',
'%nscd-default-configuration', and '%nscd-default-caches'.