previous proto struct was kept.

outstanding queries, and processing a DNS response packet was O(n) in the
number of outstanding queries. To speed things up in Google, we added a few circular,
doubly-linked lists of queries that are hash-bucketed based on
the attributes we care about, so most important operations are now O(1).

It might be that the number of buckets are higher than most people would need,
but on a quick calculation it should only be 100kB or so even on a 64-bit
system, so I've let it stay as-is.

Read and process as many packets as possible in read_udp_packets, to avoid having to run the entire event loop once per packet. (Patch from the Google tree.)

There are two different places in write_tcp_data() that advance the send_queue; however, they are slightly different and only the first one properly uses a while loop. Consolidate both into a single function that DTTR. (Patch from the Google tree.)

Reject names that are longer than 255 characters, to avoid problems with strict or buggy DNS server implementations. (Patch from the Google tree)

In ares_mkquery, make sure we set buflen and buf to reasonable values if there's an error. (Patch from the Google tree)

notifier callback(s).

and API changes in the progress callback (and possibly more coming up from
Steinar)

Always register for TCP events even if there are no outstanding queries, as the other side could always close the connection, which is a valid event which should be responded to.

Support a few more socket options, and refactor the option setting a bit. (Patch from the Google tree.)

Make the query callbacks return the number of timeouts that happened during the execution of a query, and update documentation accordingly. (Patch from the Google tree.)

Three fixes in one commit (sorry): a) Take care of the tcpbuf if it ends while queued for transmission, note broken servers and close them in the main loop, and store TCP socket generation number in order not to send the same query twice over the same socket.

is non-NULL before we FD_CLR

both to occur

variables to avoid shadowing global declarations.