Actually use the log facility for reporting evdns problems.

Fixes issue #63.  Also refactors the evdns logging and log backend a
bit, so that it wastes a little less code.
When we seed from /proc/sys/kernel/random/uuid, count it as success

Found by Joseph Spadavecchia
Document that arc4random is not a great cryptographic PRNG.
Merge remote-tracking branch 'origin/patches-2.0'
Merge branch '21_evdns_log_debug'