Added multicast join/leave handling on per-interface basis.
For testing purposes, added options to manually specify joined/master interfaces (they work only partially, though, as without OSPF, there is no info about valid prefixes. Oh well.)
Added relatively elaborate sanity check to check cache<>own propagation lifecycle.
Fixed sendto to work correctly (just passing along sendto method does not obviously work, sigh).
Fixed? one assertion for which there was no unit test, hopefully. At least, nothing should be damaged by this.
TODO update.