collectd.conf: Fix default packet size of the network plugin.

Fixes: #710
Statsd: support samplerate field in timing metric types

Fixes "Unable to parse line" bug, often seen receiving stats from
OpenStack Swift. Should fix GH issue #461
EL <6 provide perl-ExtUtils-Embed with base perl

Conflicts:
	contrib/redhat/collectd.spec
collectd.conf(5): Improve documentation of LoadPlugin.

Mention AutoLoadPlugin in the relevant places. Add a <Plugin /> block
for the "df" plugin to make it easier to spot that it is preceded by a
<LoadPlugin /> *block*.

Fixes: #715
collectd.conf(5): Improve AutoLoadPlugin documentation.

Make it clear that plugins without a <Plugin /> block will still need a
LoadPlugin line.

References: #715
java plugin: Make sure cjni_thread_detach() is called on all paths.

Each call to cjni_thread_attach() much be accompanied by
a call to cjni_thread_detach(). Some error handling cases were missing
the call, potentially locking the plugin up.
GenericJMXConfConnection: Remove unused imports.
RPM specfile: update changelog without incrementing release number
Merge branch 'collectd-5.3' into collectd-5.4

Conflicts:
	contrib/redhat/collectd.spec
src/utils_rrdcreate.c: Free "args".

Thanks to Yves Mettier for pointing this out!

Fixes: #661
python plugin: Don't create empty meta_data_t objects.

Fixes: #716
src/utils_format_json.c: Handle empty meta_data_t gracefully.

Previously, `meta != NULL` and `keys_num == 0` was possible and would
result in "{}", which is not valid JSON.

Fixes: 716
src/meta_data.c: If the meta_data_t is empty, avoid calling malloc(0).
Merge remote-tracking branch 'github/collectd-5.3' into collectd-5.3
curl plugin: Use the utility functions for config handling.
src/utils_match.[ch]: Implement match_value_reset().

This is called from the curl and memcachec plugins. Previously, gauge
average, minimum and maximum values were calculated since the start of
the daemon, rather than per-interval. This is not the documented
functionality.

Fixes: #663
network plugin: Improve client connecting behavior.

This moves the socket creation logic so it's called from
networt_send_buffer_plain(). This allows us to recover after network
failures or when collectd was started before the network was available.

Fixes: #627
Merge branch 'collectd-5.3' into collectd-5.4

Conflicts:
	src/curl.c
Merge branch 'collectd-5.4'
disk plugin: Add metric for pending I/O operations.

This is only supported on Linux right now.

Fixes: #705