#7 muninlite on DD-WRT

[CK]

Muninlite worked great on OpenWRT but I encountered some difficulties on DD-WRT, as some plugins behaved differently:
* The if_ plugins would always exit with:
munin_set_var_loc: Setting unknown option '_tmp_munin_node_' at example.org;router.example.org:if_etherip0
* The df_ plugin would return an empty set because "df -P /" did not work - but "df -P" did.
* While I was on it, I did some whitespace cleanup, hence the bigger size of the patch:

munin-node.in | 142 +++++++++++++++++++++++++++-----------------------------
plugins/df | 31 +++++-------
plugins/if_ | 47 +++++++++---------
plugins/if_err_ | 33 ++++++-------
4 files changed, 124 insertions(+), 129 deletions(-)

[CK]

apply with -p0