Added mentioning about pdns_remotebackend libs
Merge pull request #1156 from cmouse/docs-mention-pdns_remotebackend

Added mentioning about pdns_remotebackend libs
add timeout&gracetime flags to gmysql
withhold some exceptions inside gsql
push gmysql connection logic down, to make sure connection failures do not prohibit launch
implement gracetime
add readonly mode for g(my)sql
fix error message in GSQLBackend::isMaster
fix accidental lineswap
add d_readonly check to new gsql methods (post-rebase)
log user in query log
do not error out when we can just say no in a friendly way
clear upstream caches after a successful query right after expiring gracetime
make d_prefix public for logging in gsql
add experimental-consistent-backends flag

Conflicts:
	pdns/common_startup.cc
add host/database to query logging
tolerate domain list failure in master or slave mode
avoid hitting all backends for getSOA
return SERVFAIL when all backends are down