Plugin df free space as percentage.

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

And fix indentation.
df plugin: Rename the percent metrics.

* Change type to "percent".
* Use "<disk>-bytes" and "<disk>-inodes" as plugin instance. This way we're
  able to use "percent" for both.
* Remove one level of indentation.
* Make casting more explicit (e.g. don't divide a float by a size_t).
collectd.conf(5): Minor fixes.
curl plugin: Fix compiler warning.

The compiler thinks the "start" variable may be used uninitialized.
Merge branch 'vb/df'
Merge branch 'yaccz/curl-status'