olsr: allow lazy-plugin-naming: e.g. olsrd_txtinfo (not olsrd_txtinfo.so.1.2)

overload init-skript's olsrd_write_loadplugin() with new function
find_most_recent_plugin_libary() - so now we can mix 'exact' and lazy
names. This change is backward compatible and now we have a better
migration strategy. This topic was hot again, after the latest updates
of a lot of plugins, resulting in non-working configs...