Makefile: split out clean of plugins into separate targets
Makefile: split out clean of plugins into separate targets

Otherwise repeated plugin builds are unnecessarily slow.

Signed-off-by: Ferry Huberts <66e11f9f5d965b69497c7e73d5e808f8b13c1218@pelagic.nl>

sebkur/olsrd,diogomg/olsrd,duydb2/olsr,diogomg/olsrd-binary-heap,acinonyx/olsrd,zioproto/olsrd,nolith/olsrd,diogomg/olsrd,ninuxorg/olsrd,sebkur/olsrd,ninuxorg/olsrd,nolith/olsrd,sebkur/olsrd,diogomg/olsrd,diogomg/olsrd-binary-heap,cholin/olsrd,zioproto/olsrd-gsoc2012,diogomg/olsrd,cholin/olsrd,diogomg/olsrd-binary-heap,tdz/olsrd,diogomg/olsrd-binary-heap,zioproto/olsrd,cholin/olsrd,nolith/olsrd,duydb2/olsr,tdz/olsrd,acinonyx/olsrd,servalproject/olsr,ninuxorg/olsrd,zioproto/olsrd,duydb2/olsr,duydb2/olsr,sebkur/olsrd,zioproto/olsrd-gsoc2012,acinonyx/olsrd,zioproto/olsrd,servalproject/olsr,ninuxorg/olsrd,acinonyx/olsrd,servalproject/olsr,nolith/olsrd,servalproject/olsr,diogomg/olsrd,zioproto/olsrd-gsoc2012,acinonyx/olsrd,diogomg/olsrd-binary-heap,sebkur/olsrd,zioproto/olsrd,diogomg/olsrd-binary-heap,nolith/olsrd,ninuxorg/olsrd,zioproto/olsrd-gsoc2012,diogomg/olsrd-binary-heap,sebkur/olsrd,diogomg/olsrd,duydb2/olsr,diogomg/olsrd,duydb2/olsr,tdz/olsrd,duydb2/olsr,zioproto/olsrd-gsoc2012,servalproject/olsr,zioproto/olsrd-gsoc2012,cholin/olsrd,duydb2/olsr,tdz/olsrd,servalproject/olsr,tdz/olsrd,cholin/olsrd