Merge pull request #3159 from rpv-tomsk/collectd-usercache

check_uptime: New plugin, based on new cache_event callback.

diff --cc Makefile.am
Simple merge

diff --cc configure.ac
Simple merge

diff --cc src/collectd.conf.in
Simple merge

diff --cc src/collectd.conf.pod
Simple merge

diff --cc src/daemon/plugin.c
Simple merge

diff --cc src/daemon/plugin.h
Simple merge

diff --cc src/daemon/utils_cache.c
Simple merge