munin-update with max_processes=1 is the serial option

... while max_processes=0 does what it says - and spins with 100% cpu doing nothing.
Clean field names

Non-clean field names cause problems with drawing, e.g. when there are spaces
or dashes in the process name. This commit cleans the field name by using the
appropriate support module. For more information, see:

http://munin-monitoring.org/wiki/notes_on_datasource_names
Added documentation for 'Clean field names'
Clean procargs and procuser as well

Github user @leeclemens reported that procargs should be cleaned as well and
rightly so. I took this opportunity to clean procuser as well, since usernames
could have periods (even though people should probably avoid that, if possible).

Tested procargs with 'python example.py', this gave expected results.
Allow spaces int he mount point in the plugin 'df'
fix irqstats
Only get non-parameter parts of $ARGV to @graphs (Fix #1418)

* munin-graph expects ether no cli parameter at all or a specific string which
  graph to render. When called with --debug or any other parameter it throws
  error messages to the log and does not render the graphs.

  This patch changes this. It pushes only params from @ARGV to @graphs which
  doesn't start with --.
  See trac ticket #1418 .
Merge branch 'pr/125' into devel

Conflicts:
	plugins/node.d.linux/proc.in
Merge branch 'pr/130' into devel
Merge remote branch 'pull/144' into devel
Merge remote branch 'pull/137' into devel

Conflicts:
	plugins/node.d.linux/df.in
Merge remote branch 'pull/154' into devel