nut: add dev headers, nut-web-cgi and nut-avahi-service, bugfix

Headers are required by collectd as mentioned in #1801. This is the nut portion based on dwmw2@d636841cd1d1dfab04cb509520c082738ddfb2ea
Happy to merge with 15.05 as per #1803.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
[martin.p.rowe@gmail.com: condensed InstallDev lines]

Added package nut-web-cgi based on demorfi@7e340f47944ff4a9c49d3b1dc6c1d9d965cd344c. Closes #1614.
Pending signoff by @demorfi
[martin.p.rowe@gmail.com: simplified implementation, no changes to Config.in]

Added package nut-avahi-service similar to other implementations in #618
Bugfix to remove redundant NUT_DRIVER_SERIAL config
Bugfix to make UPSLOG config actually install (requires PKG_RELEASE bump)
Some code tidy-ups
Signed-off-by: Martin Rowe <martin.p.rowe@gmail.com>

net/nut/files/nut.service

@@ -0,0 +1,34 @@
+<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
+<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
+
+<!--
+  This file is part of NUT - Network UPS Tools
+
+  NUT is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  NUT is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with NUT; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+  02111-1307 USA.
+-->
+
+<!-- See avahi.service(5) for more information about this configuration file -->
+
+<service-group>
+
+  <name replace-wildcards="yes">%h</name>
+
+  <service>
+    <type>_nut._tcp</type>
+    <port>3493</port>
+  </service>
+
+</service-group>