warnings, one C99 thing and the bad pointer sent to the callback

CURLOPT_OPENSOCKETDATA to set a callback that allows an application to replace
the socket() call used by libcurl. It basically allows the app to change
address, protocol or whatever of the socket. (I also did some whitespace
indent/cleanups in lib/url.c which kind of hides some of these changes, sorry
for mixing those in.)

CURLE_PEER_FAILED_VERIFICATION (standard CURL_NO_OLDIES style), and made this
return code get used by the previous SSH MD5 fingerprint check in case it
fails.

CURLOPT_SSH_HOST_PUBLIC_KEY_MD5 and the curl tool --hostpubmd5. They both make
the SCP or SFTP connection verify the remote host's md5 checksum of the public
key before doing a connect, to reduce the risk of a man-in-the-middle attack.

function init_id_key() under low memory conditions.

Added test case 1008 to verify. Note that #47 is still there.

attempt to force smaller bits to get read by clients.

CURLOPT_POST301 written by Philip Langdale

it gets passed the initial value as an argument.

supported range.

in as argument!

target called 'filecheck' so that if you run 'make filecheck' in this directory
it'll check if the local files are also mentioned in the Makefile.am so that
they are properly included in release archives!

function do wrong on all input bytes that are >= 0x80 (decimal 128) due to a
signed / unsigned mistake in the code. I fixed it and added test case 543 to
verify.

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.)