The 'no-negcache?' option is mapped to the '--no-negcache' command-line
argument directly, but we're in the scheme world, where the general guideline
is to avoid double-negations in identifiers.
* gnu/services/dns.scm <dnsmasq-configuration>: Replace the 'no-negcache?'
field with 'negative-cache?'.
* doc/guix.texi (DNS Services)[Dnsmasq Service]: Adjust accordingly.
* gnu/services/dns.scm (dnsmasq-service-type): New variable.
(<dnsmasq-configuration>): New record type.
(dnsmasq-shepherd-service): New procedure.
* doc/guix.texi (DNS Services): Document it.
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