Merge pull request #307 from adamdunkels/push/fragmentation

6lowpan fragmentation fix
Merge pull request #330 from adamdunkels/push/faster-collect-lossy

Faster collect-lossy travis test
Added new neighbor-table module, a centralized place where to store all data about neighbors, indexed by link-layer address. Meant for use in other Contiki modules such as rpl, ds6, ds6-route, phase, neighbor-info.
Make phase module use neighbor-table.
Make DS6 neighbors use neighbor-table, and move all DS6 neighbor management from uip-ds6 to a new uip-ds6-neighbor module.
Make uip-ds6-route use neighbor table. Instead of storing a global list of routing entries that contain both the next hop and the destination, we have a separate list of reachable destination for each neighbor in the global table.
Make RPL use neighbor tables. RPL locks the neighbor used as preferred parent.
Moved ETX management from neighbor-info to rpl-of-etx. Avoids conversions between different fixed point representations, and simplifies neighbor management. Makes more clear how default-ETX and noack-ETX actually affect the rank. Removed neighbor-info and neighbor-attr.
Removed now unused per-module neighbor table size configs. Use NEIGHBOR_CONF_MAX_NEIGHBORS instead.
Port apps, examples, platforms and tools so they use the new neighbor and route API.
Fix naming issues and includes in uip-ds6-nbr.h