Fixed syntax errors in Coverity model.
Fixed Coverity model for munmap() to take errors into account.
roots_fill_closest(): avoid memory leak on the error path.

When we got an I/O error whilst filling approximate roots, we were returning 0
which was wrong: we may had already filled some nodes in the vector (but less
than KDA_K) and we were not cleaning the possibly created patricia tree.
Factorized creation of unique random GUIDs.
Use "guid_t" instead of "struct guid".
Coverity model: vmm_valloc() can fail and return MAP_FAILED (-1) on errors.
DHT: account bucket splits and merges.
forget_hashlist_node(): force node status to KNODE_UNKNOWN, unconditionally.

When the node is leaving the routing table, it must be flagged as such to
prevent further assertion failures when its refcount reaches 0 (a node in the
routing table could not reach this status unless there was a refcount bug).

The downside of that change is that we now need to forcefully reset the
status of the nodes in the split/merged buckets according to the list they
belong to, once the original bucket being split/merged has been cleared.

However, this will prevent subtle assertion failures when the nodes referred
to by the split/merged buckets are also part of an active DHT lookup.
Updated the set of translatable strings.