Make test "endtoend" pass on 'slow' systems

auto_test/crypto_test.c:
- test "endtoend": increased timeout from default ~5s to 15s, making it pass on slower systems
- signed/unsiged warning fixed by cast
Tests of state loading/saving lead to two fixes for DHT.c and util.c

util.c:
- fix in empty section at the end of the state, showed as bug when having an empty name

DHT.c:
- fix in saving less data than originally announced, showed as bug when not having reached any clients ever (no clients or only with timestamp of zero)
Merge remote-tracking branch 'upstream/master' into MessengerLoadSave
Merge pull request #584 from FullName/MessengerLoadSave

Tests of state loading/saving lead to two fixes for DHT.c and util.c
Merge pull request #583 from FullName/TestCryptoSlow

Make test "endtoend" pass on 'slow' systems