cgi-graph: also accept csv & json extensions
cgi-graph: Adding csv output
cgi-graph: adding json output
cgi-graph: adding xml output
cgi-graph: fix typo
cgi-graph: fix xml output
snmp__df.in: convert to use Munin::Plugin::SNMP.

This basically removes lots of boilerplate code that is already
available in that module, and simplifies the plugin a lot. It does not
change the output beside for dropping the final _ in the services'
names.
Merge branch 'gfx-textual-output' into devel