- Mapaddress
- Postdescriptor
- GetInfo on descriptors

Required changes elsewhere:
- Keep the most recent running_routers_t in the routerlist_t. That way we
  can learn about new routers and remember whether we were last told that
  they were up or down.  Also enables more simplifications.
- Keep the signed descriptor inside routerinfo_t.  This makes
  descriptor_entry_t in dirservers.c unneeded.
- Rename AddressMap (the verb) to MapAddress. Keep AddressMap as a noun.
- Check addresses for plausibility before mapping them.


svn:r3696