varnish plugin: Make sure the argument passed to VSM_n_Arg() is not NULL.

Fixes Github issue 202.
Updating data source for collectd v5, see https://collectd.org/wiki/index.php/V4_to_v5_migration_guide

Signed-off-by: Florian Forster <octo@collectd.org>
zfs_arc plugin: Fix the type used for mutex misses.

Thanks to Yves Mettier for pointing this out!
src/types.db: Remove the maximum value from "timeleft".
ethstat plugin: Fix the map lookup.

Previously, a pointer into the configuration structure was used to look
up the mappings. Because the configuration structure is freed or
otherwise modified, this does not work as intended (and may actually
lead to a segmentation fault when unlucky).

For completeness sake, a shutdown callback was added to free the used
memory on exit.

Fixes Github issue 224.
Fixed a small typo in the ethstat plugin

Signed-off-by: Florian Forster <octo@collectd.org>
dbi plugin: Replace cdbi_config_set_string() with cf_util_get_string().
Merge branch 'collectd-4.10' into collectd-5.1
Merge branch 'collectd-5.1' into collectd-5.2
write_graphite: Decrease a buffer size.

If the buffer is too large, it is possible that the message cannot be
send using the send buffer, leading to a failed assertion in
wg_send_message().

Fixes Github issue #226. Thanks to @bwhaley for reporting this.
Merge remote-tracking branch 'origin/collectd-5.2' into collectd-5.2