varnish plugin: missing definition in default config
varnish plugin: add missing fields

This commit adds a large number of fields exported by the varnish stats
interface which have not previously been collected. A number are still missing,
as it is not immediately obvious which stat group they should go in:

    accept_fail
    client_drop_late

and, from Varnish 3.X:

    vmods
    n_gzip
    n_gunzip

In addition, there are a number of fields which were added at the end of the 2.X
series, but in the absence of a way of detecting whether we're compiling against
2.0.X or 2.1.X, are necessarily disabled when compiling against 2.X:

    dir_dns_lookups
    dir_dns_failed
    dir_dns_hit
    dir_dns_cache_full
    backend_retry
    fetch_1xx
    fetch_204
    fetch_304
add MeasureResponseCode refs #319
varnish plugin: update config docs for new collectors
src/plugin.c: Make plugin_load() idempotent, i.e. don't load plugins twice.

Previously, multiple 'LoadPlugin "foo"' lines would dlopen the same .so file
twice and call its module_register function twice. This would eventually result
in complaints about callbacks with the same name being registered. With this
patch each plugin is only loaded only once, allowing people to write "self
contained" configuration segments.

Thanks to Tim Bunce for suggesting this!

Github: #333
collectd.conf(5): Document the new "LoadPlugin" behavior.

Github: #333
src/plugin.c: Move the perl and python "global" magic to plugin_load().

The config file handling is really not the best place to have this. Also,
the feature I'm working on would have to copy this magic if left in the
config code, and I *really* don't want that.
src/plugin.c: Fix a comment regarding duplicate plugin_load() calls.
src/configfile.c: Add the "AutoLoadPlugin" option.

When enabled, <Plugin ...> blocks will automatically load plugins.
Thanks to Tim Bunce for suggesting this!

Github: #333
Merge branch 'more-varnish-stats'
curl plugin: Fix compile issue (long vs. long*).
curl plugin: Remove the curl-only auxiliary configuration functions.
curl plugin: Don't abort when reading the response code failed.
curl plugin: Use cdtime to calculate response times.
Merge branch 'yaccz/curl-status'
allow for non-root user to run script.
As collectdmon handles its pidfile, this would require to change
COLLECTMONPIDIR to something else than only-root writeable /var/run

Change-Id: I45d2de9dcc976f3b1e18cef5b6b78eeca1d270b2
Signed-off-by: Florian Forster <octo@collectd.org>
contrib/redhat/init.d-collectd: Rename variable to …PIDDIR.

Github: #298
Implement ARC data collection on FreeBSD.
Plugin df free space as percentage.

Signed-off-by: Florian Forster <octo@collectd.org>
Plugin df: ReportPercentage