Use windows vsnprintf fixup logic on all windows environments

Previously I'd relied on mingw to provide a vsnprintf with a
conformant return value.  But it appears that some mingw
environments don't do that.
Merge remote-tracking branch 'origin/patches-2.0'
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.
Fix SEGFAULT after evdns_base_resume if no nameservers installed.

If there is no nameservers installed, using
evdns_base_nameserver_ip_add(), than evdns_base_resume() will SEGFAULT,
because of NULL dereference in evdns_requests_pump_waiting_queue()

Conflicts:
	evdns.c
restore the comment
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'
Merge remote-tracking branch 'public/pr/79' into patches-2.0
Merge remote-tracking branch 'origin/patches-2.0'