Unbreak type_inst value in collectd psql view.

Signed-off-by: Florian Forster <octo@collectd.org>
threshold plugin: Fix the "Interesting" configuration option.

Signed-off-by: Florian Forster <octo@collectd.org>
collectd-threshold(5): Correct the description of the "Interesting" config option.
src/common.c: Reimplement format_name for performance.

This is used from uc_update(), i.e. for every value list dispatched, and was
one of the most expensive functions thanks to snprintf().

This reduces total time spent in the format_name() function from 7.78% to 1.89%
during a network stress test.
csv plugin: Re-implement value_list_to_filename().

The new implementation is faster, because it doesn't use snprintf().
rrdtool, rrdcached plugins: Re-implement value_list_to_filename().

Faster version without snprintf().
Merge branch 'collectd-5.2' into collectd-5.3